World War II, or the Second World War, was a global military conflict, the joining of what had initially been two separate conflicts. The first began in Asia in 1937 as the Second Sino-Japanese War; the other began in Europe in 1939 with the German invasion of Poland.
This global conflict split the majority of the world's nations into opposing military alliances: the Allies which in the beginning of the war consisted of Great Britain and France (later the Soviet Union and the United States), and the Axis powers with Germany, Italy, and Japan as its members. It involved the mobilization of over 100 million military personnel, making it the most widespread war in history, and placed the participants in a state of "total war", erasing the distinction between civil and military resources. This resulted in the complete activation of a nation's economic, industrial, and scientific capabilities for the purposes of the war effort. Over 60 million people, the majority of them civilians, were killed, making it the deadliest conflict in human history. The financial cost of the war is estimated at about a trillion 1944 U.S. dollars worldwide, making it the most costly war in capital as well as lives.
The Allies were victorious, and, as a result, the Soviet Union and the United States emerged as the world's leading superpowers. This set the stage for the Cold War, which lasted for the next 45 years. The United Nations was formed in hopes of preventing another such conflict. The self determination spawned by the war accelerated decolonization movements in Asia and Africa, while Europe itself began moving toward integration.
In the aftermath of World War I, the defeated German Empire signed the Treaty of Versailles. This caused Germany to lose 13% of its national territory and prohibited the annexation of Austria, Czechoslovakia, Poland and Danzig, and mandated German armed forces number no more than 100,000 troops. Some of the Treaty's prohibitions were of conscription, manufacturing of weapons, import and export of weapons, and imposed massive reparations on Germany.
Russia's Civil war led to the creation of the Soviet Union which soon was under the control of Joseph Stalin. In Italy, Benito Mussolini seized power as a fascist dictator promising to create a "New Roman Empire." The ruling Kuomintang (KMT) party in China launched a unification campaign against rebelling warlords in the mid-1920s, but was soon embroiled in a civil war against its former Chinese communist allies. In 1931, an increasingly militaristic Japanese Empire, which had long sought influence in China as the first step of its right to rule Asia, used the Mukden Incident as justification to invade Manchuria; the two nations then fought several small conflicts until the Tanggu Truce in 1933.
National Socialist Adolf Hitler became the leader of Germany in January 1933. He began a massive rearming campaign. This worried France and the United Kingdom, who had lost much in the previous war, as well as Italy, which saw its territorial ambitions threatened by those of Germany. To secure its alliance, the French allowed Italy a free hand in Ethiopia, which Italy desired to conquer. The situation was aggravated in early 1935 when the Saarland was legally reunited with Germany and Hitler repudiated the Treaty of Versailles, speeding up remilitarization and introducing conscription. Hoping to contain Germany, the United Kingdom, France and Italy formed the Stresa Front. The Soviet Union, concerned due to Germany's goals of capturing vast areas of eastern Europe, concluded a treaty of mutual assistance with France.
Before taking effect, the Franco-Soviet pact required to go through the League of Nations but was essentially toothless and in June of 1935, the United Kingdom made an independent naval agreement with Germany easing prior restrictions. The United States, concerned with events in Europe and Asia, passed the Neutrality Act in August. In October Italy invaded Ethiopia, with Germany the only major European nation supporting her invasion. Italy then revoked objections to Germany's goal of making Austria a satellite state.
In direct violation of the Versailles and Locarno treaties, Hitler remilitarized the Rhineland in March of 1936. He received little response from other European powers. When the Spanish Civil War broke out in July, Hitler and Mussolini supported fascist Generalísimo Francisco Franco in his civil war against the Soviet-supported Spanish Republic. Both sides used the conflict to test new weapons and methods of warfare.
With tensions mounting, efforts to strengthen or consolidate power were made. In October, Germany and Italy formed the Rome-Berlin Axis and a month later Germany and Japan, each believing communism and the Soviet Union in particular to be a threat, signed the Anti-Comintern Pact, which Italy would join in the following year. In China, the Kuomintang and communist forces agreed on a ceasefire to present a united front to oppose Japan.
In mid-1937, following the Marco Polo Bridge Incident, Japan began a full invasion of China. The Soviets quickly lent support to China, effectively ending China's prior cooperation with Germany. Starting at Shanghai, the Japanese pushed Chinese forces back, capturing the capital Nanjing in December. In June of 1938 Chinese forces stalled the Japanese advance by flooding the Yellow River. Though this bought time to prepare their defenses at Wuhan, the city was still taken by October. During this time, Japanese and Soviet forces engaged in a minor skirmish at Lake Khasan; in May of 1939, they became involved in a more serious border war.
In Europe, Germany and Italy were becoming bolder. In March 1938, Germany annexed Austria, again provoking little response from other European powers. Encouraged, Hitler began making claims on the Sudetenland; France and Britain conceded these for a promise of no further territorial demands. Germany soon reneged, and in March 1939 fully occupied Czechoslovakia.
Alarmed, and with Hitler making further demands on Danzig, France and Britain guaranteed their support for Polish independence; when Italy conquered Albania in April, the same guarantee was extended to Romania and Greece. The Soviet Union also attempted to ally with France and Britain, but was rebuffed due to western suspicions about Soviet motives and capability. Shortly after the Franco-British pledges to Poland, Germany and Italy formalized their own alliance with the Pact of Steel; following this, in a move that shocked all other major powers, Germany and the Soviet Union concluded a non-aggression pact, including a secret agreement to split Poland and eastern Europe between them.
By the start of September 1939, the Soviets had routed Japanese forces and the Germans invaded Poland. France, Britain, and the countries of the Commonwealth declared war on Germany but lent little support other than a small French attack into the Saarland. In mid-September, after signing an armistice with Japan, the Soviets launched their own invasion of Poland. By early October, Poland had been divided between Germany and the Soviet Union. During the battle in Poland, Japan launched its first attack against Changsha, a strategically important Chinese city, but was repulsed by early October.
Following the invasion of Poland, the Soviets began moving troops into the Baltic region. Finnish resistance in late November led to a four-month war, ending with Finnish concessions. France and the United Kingdom, treating the Soviet attack on Finland as tantamount to entering the war on the side of the Germans responded to the Soviet invasion by supporting its expulsion from the League of Nations. Though China had the authority to veto such an action, it was unwilling to alienate itself from either the Western powers or the Soviet Union and instead abstained. The Soviet Union was displeased by this course of action and as a result suspended all military aid to China. By mid-1940, the Soviet Union's occupation of the Baltics was completed with the installation of pro-Soviet governments.
In Western Europe, British troops deployed to the Continent, but neither Germany nor the Allies launched direct attacks on the other. In April, Germany invaded Denmark and Norway to secure shipments of iron-ore from Sweden which the allies would try to disrupt. Denmark immediately capitulated, and despite Allied support Norway was conquered within two months. British discontent over the Norwegian campaign led to the replacement of Prime Minister Neville Chamberlain by Winston Churchill on May 10, 1940.
On that same day, Germany invaded France and the Low Countries. Using blitzkrieg tactics, the Netherlands and Belgium were overrun and British troops were forced to evacuate the continent, abandoning their heavy equipment by the end of the month. On June 10th, Italy invaded, declaring war on both France and the United Kingdom; twelve days later France surrendered and was soon divided into German and Italian occupation zones, and an unoccupied rump state under the Vichy Regime. In early July, the British attacked the French fleet in Algeria to prevent their seizure by Germany.
With France neutralized, Germany began an air superiority campaign over Britain to prepare for an invasion and enjoyed success against an over-extended Royal Navy, using U-boats against British shipping in the Atlantic. Italy began operations in the Mediterranean, initiating a siege of Malta in June, conquering British Somaliland in August, and making an incursion into British-held Egypt in early September. Japan increased its blockade of China in September by seizing several bases in the northern part of the now-isolated French Indochina.
Throughout this period, the neutral United States took measures to assist China and the Western Allies. In November 1939, the American Neutrality Act was amended to allow Cash and carry purchases by the Allies. During 1940, the United States implemented a series of embargos, including oil, iron, steel and mechanical parts, against Japan; in September it agreed to a trade of American destroyers for British bases.
At the end of September the Tripartite Pact between Japan, Italy and Germany formalized the Axis Powers. The pact stipulated, with the exception of the Soviet Union, any country not in the war which attacked any Axis Power would be forced to go to war against all three. The Soviet Union expressed interest in joining the Tripartite Pact, sending a modified draft to Germany in November and offering a very German-favourable economic deal; while Germany remained silent on the former, they accepted the latter. Regardless of the pact, the United States continued to support the United Kingdom and China by introducing the Lend-Lease policy and creating a security zone spanning roughly half of the Atlantic Ocean where the United States Navy protected British convoys.
In October, Italy invaded Greece but within days were repulsed and pushed back into Albania, where a stalemate soon occurred. Shortly after this, in Africa, Commonwealth forces launched offensives against Libya and Italian East Africa. By early 1941, with Italian forces having been pushed back into Libya by the Commonwealth, Churchill ordered a dispatch of troops from Africa to bolster the Greeks. The Italian Navy also suffered significant defeats, with the Royal Navy putting three Italian battleships out of commission via carrier attack at Taranto, and several more warships neutralized at Cape Matapan.
The Germans soon intervened to assist Italy. Hitler sent German forces to Libya in February and by the end of March they had launched an offensive against the diminished Commonwealth forces. In under a month, Commonwealth forces were pushed back into Egypt with the exception of the besieged port of Tobruk. The Commonwealth attempted to dislodge Axis forces in May and again in June, but failed on both occasions. In early April the Germans similarly intervened in the Balkans, invading Greece and Yugoslavia; here too they made rapid progress, eventually forcing the Allies to evacuate after Germany conquered the Greek island of Crete by the end of May.
The Allies did have some successes during this time though. In the Middle East, Commonwealth forces first quashed a coup in Iraq which had been supported by German aircraft from bases within Vichy-controlled Syria, then, with the assistance of the Free French, invaded Syria and Lebanon to prevent further such occurrences. In the Atlantic, the British scored a much needed public morale boost by sinking the German flagship Bismarck. Perhaps most importantly, the Royal Air Force had successfully resisted the Luftwaffe's assault, and on May 11, 1941, Hitler called off the bombing campaign over Britain.
In Asia, in spite of several offensives by both sides, the war between China and Japan was stalemated by 1940. In August of that year, Chinese communists launched an offensive in Central China; in retaliation, Japan instituted harsh measures in occupied areas to reduce human and material resources for the communists. Mounting tensions between Chinese communist and nationalist forces culminated in January 1941, effectively ending their co-operation.
With the situation in Europe and Asia relatively stable, Germany, Japan and the Soviet Union made preparations. With the Soviets wary of mounting tensions with Germany and the Japanese planning to take advantage of the European War by seizing resource-rich European possessions in Southeast Asia the two powers signed a neutrality agreement in April, 1941. By contrast the Germans were steadily making preparations for an attack on the Soviet Union, amassing forces on the Soviet border, particularly in Finland and Romania.
In late June, Germany, along with other European Axis members and Finland, invaded the Soviet Union. They made significant gains into Soviet territory, inflicting a large numbers of casualties, and by the start of December had almost reached Moscow, with only the besieged cities of Leningrad and Sevastopol behind their front-lines left unconquered. With the onset of a fierce Soviet winter though, the Axis offensive was ground to a halt and the Soviets launched a counter-offensive using reserve troops brought up from the border near Japanese Manchukuo.
Following the German attack on the Soviets, the United Kingdom began to regroup. In July, the United Kingdom and the Soviet Union formed a military alliance against Germany and shortly after jointly invaded Iran to secure the Persian Corridor and Iran's oilfields. In August, the United Kingdom and United States jointly issued the Atlantic Charter, a vision for a post-war world which included "the right of all peoples to choose their form of government". In November, Commonwealth forces launched a counter-offensive in the desert, reclaiming all gains the Germans and Italians had made.
In Asia, Japan was preparing for war. The Imperial General Headquarters plan was to create a large perimeter stretching into the Central Pacific in order to facilitate a defensive war while exploiting the resources of Southeast Asia; to prevent intervention while securing the perimeter it was further planned to neutralize the United States Pacific Fleet on the outset. In preparation, Japan seized military control of southern Indochina in July, 1941; an action the United States, United Kingdom and other western governments responded to by freezing all Japanese assets. On December 7th Japan attacked British, Dutch and American holdings with near simultaneous offensives against Southeast Asia and the Central Pacific, including an attack on the American naval base of Pearl Harbor.
These actions prompted the United States, United Kingdom, China, and other Western Allies to declare war on Japan. Italy, Germany, and the other members of the Tripartite Pact responded by declaring war on the United States. In January, the United States, United Kingdom, Soviet Union and China, along with twenty-two smaller or exiled governments, issued the Declaration by United Nations, affirming the Atlantic Charter and formalizing their alliance against the Axis Powers. The Soviet Union did not adhere fully to the declaration though, as they maintained their neutrality agreement with Japan and exempted themselves from the principle of self-determination.
The Axis Powers, however, were able to continue their offensives. Japan had almost fully conquered Southeast Asia with minimal losses by the end of April, 1942, chasing the Allies out of Burma and taking large numbers of prisoners in the Philippines, Malaya, Dutch East Indies and Singapore. They further bombed the Allied naval base at Darwin, Australia and sunk significant Allied warships not only at Pearl Harbor, but also in the South China Sea, Java Sea and Indian Ocean. The only real successes against Japan were a repulsion of their renewed attack on Changsha in early January, 1942, and a psychological strike from a bombing raid on Japan's capital Tokyo in April.
Germany was able to regain the initiative as well. Exploiting American inexperience with submarine warfare, the German Navy sunk significant resources near the American Atlantic coast. In the desert, they launched an offensive in January, pushing the British back to positions at the Gazala Line by early February. In the Soviet Union, the Soviet's winter counter-offensive had ended by March. In both the desert and the Soviet Union, there followed a temporary lull in combat which Germany used to prepare for their upcoming offensives.[79
In early May, Japan initiated operations to capture Port Moresby via amphibious assault and thus sever the line of communications between the United States and Australia. The Allies, however, intercepted and turned back Japanese naval forces, preventing the invasion. Japan's next plan, motivated by the earlier bombing on Tokyo, was to seize the Midway Atoll as this would seal a gap in their perimeter defenses, provide a forward base for further operations, and lure American carriers into battle to be eliminated; as a diversion, Japan would also send forces to occupy the Aleutian Islands. In early June, Japan put their operations into action but the Americans, having broken Japanese naval codes in late May, were fully aware of the Japanese plans and force dispositions and used this knowledge to achieve a decisive victory over the Imperial Japanese Navy. With their capacity for amphibious assault greatly diminished as a result of the Midway battle, Japan chose to focus on an overland campaign on the Territory of Papua in another attempt to capture Port Moresby. For the Americans, they planned their next move against Japanese positions in the southern Solomon Islands, primarily against the island of Guadalcanal, as a first step towards capturing Rabaul, the primary Japanese base in Southeast Asia. Both plans started in July, but by mid-September the battle for Guadalcanal took priority for the Japanese, and troops in New Guinea were ordered to withdraw from the Port Moresby area to the northern part of the island. Guadalcanal soon became a focal point for both sides with heavy commitments of troops and ships in a battle of attrition. By the start of 1943, the Japanese were defeated on the island and withdrew their troops.
In Burma, Commonwealth forces mounted two operations. The first, an offensive into the Arakan region in late 1942 went disastrously, forcing a retreat back to India by May of 1943. The second was the insertion of irregular forces behind Japanese front-lines in February which, by the end of April, had achieved dubious results.
On the German's eastern front, they defeated Soviet offensives in the Kerch Peninsula and at Kharkov and then launched their main summer offensive against southern Russia in June, 1942, to seize the oil fields of the Caucasus. The Soviets decided to make their stand at Stalingrad which was in the path of the advancing German armies and by mid-November the Germans had nearly taken Stalingrad in bitter street fighting when the Soviets began their second winter counter-offensive, starting with an encirclement of German forces at Stalingrad and an assault on the Rzhev salient near Moscow, though the latter failed disastrously. By early February, the German Army had taken tremendous losses; their troops at Stalingrad had been forced to surrender and the front-line had been pushed back beyond its position prior to their summer offensive. In mid-February, after the Soviet push had tapered off, the Germans launched another attack on Kharkov, creating a salient in their front-line around the Russian city of Kursk.
In the west, concerns that the Japanese might utilize bases in Vichy-held Madagascar caused the British to invade the island in early May, 1942. This success was off set soon after by an Axis offensive in Libya which pushed the Allies back into Egypt until Axis forces were stopped at El Alamein. On the Continent, Allied commandos had conducted a series of increasingly ambitious raids on strategic targets, culminating in a disastrous amphibious raid on the German held port of Dieppe. In August the Allies succeeded in repelling a second attack against El Alamein and, at a high cost, managed to get desperately needed supplies to the besieged Malta. A few months later the Allies commenced an attack of their own in Egypt, dislodging the Axis forces and beginning a drive west across Libya. This was followed up shortly after by an Anglo-American invasion of French North Africa which resulted in the region joining the Allies. Hitler responded to the defection by ordering the occupation of Vichy France, though the Vichy Admiralty managed to scuttle their fleet to prevent its capture by German forces. The now pincered Axis forces in Africa withdrew into Tunisia, which was conquered by the Allies by May, 1943.
Following the Guadalcanal Campaign, the Allies initiated several operations against Japan. In May, 1943, American forces were sent to eliminate Japanese forces from the Aleutians, and soon after began major operations to isolate Rabaul by capturing surrounding islands, and to breach the Japanese Central Pacific perimeter at the Gilbert and Marshall Islands. By the end of March, 1944, the Allies had completed both of these objectives, and additionally neutralized another major Japanese base in the Caroline Islands. In April, the Allies then launched an operation to retake Western New Guinea.
In mainland Asia, the Japanese launched two major offensives. The first, started in March, 1944, was against British positions in Assam, India and soon led to Japanese forces besieging Commonwealth positions at Imphal and Kohima; by May however, other Japanese forces were being besieged in Myitkyina by Chinese forces which had invaded Northern Burma in late 1943. The second was in China, with the goal of destroying China's main fighting forces, securing railways between Japanese-held territory, and capturing Allied airfields. By June the Japanese had conquered the province of Henan and begun a renewed attack against Changsha in the Hunan province.
In the Mediterranean, Allied forces launched an invasion of Sicily in early July, 1943. The attack on Italian soil, compounded with previous failures, resulted in the ousting and arrest of Mussolini later that month. The Allies soon followed up with an invasion of the Italian mainland in early September, following an armistice with the Allies. When this armistice was made public on September 8th, Germany responded by disarming Italian forces, seizing military control of Italian areas, and setting up a series of defensive lines. On September 12th, German special forces further rescued Mussolini who then soon established a new client state in German occupied Italy. The Allies fought through several lines until reaching the main German defensive line in mid-November. In January 1944, the Allies launched a series of attacks against the line at Monte Cassino and attempted to outflank it with landings at Anzio. By late May both of these offensives had succeeded and, at the expense of allowing several German divisions to retreat, on June 4th Rome was captured.
ww2 was already planned by hitler but his plan failed because he did not think britain would enter the war