Napoleon's weaknesses as a military leader
As time went on Napoleon lacked imagination in his plans.
E.g Wagram 1809. Borodino 1812. Also aims of Russian campaign 1812 weren't clear.
Ignored generals. E.g Napoleon ignored Davout at Borodino 1812- who tried to persuade Napoleon to outflank the Russians- however Napoleon went for a frontal attack.
Napoleon wasn't an innovator. Rejected new ideas, such as the use of rifles.
Managed campaigns from a distance at times. E.g sending orders to the Iberian Peninsular when in Austria. As he wasn't in the Peninsular he wasn't aware of situation.
So Napoleon's orders confused his generals.
Forced to fight a war on two fronts, for example Peninsular war and Austrians. Arguably making Napoleon weaker. Link 2 strengths of opponents.
Napoleon didn't appreciate difficulties when campaigning with large armies in inhospitable terrain. Iberian Peninsular hindered Fr. army's progress.
Troops couldn't live off the barren land. Furthermore in Russia (1812) the Fr. armys' supply lines were stretched.
Napoleon wouldn't trust his subordinates with their plans. Which becomes more evident as time goes on- as Napoleon becomes more arrogant. E.g Davout at Borodino 1812.
Military decline of Napoleon didn't take place at a steady rate, reasons for it vary in their importance over time.
Nature of the French army
Conscription starts to become a weakness. This is because more young conscripts have to be recruited to fill the gaps in the Fr. army. Less experienced.
Need to recruit after Russia 1812, when a new army was needed to fend off allied invasion.