Final answer:
The invasion of Russia led to a catastrophic defeat for Napoleon's Grand Army due to the Russians' scorched earth policy, logistical challenges, disease, and the brutal winter. It significantly weakened Napoleon's forces and contributed to his eventual downfall.
Step-by-step explanation:
The effect of Napoleon's invasion of Russia was disastrous for the French. Despite starting with a Grand Army of 650,000 men, the campaign failed due to the Russians employing a scorched earth policy, burning their own cities and crops to deny the French resources. As Napoleon advanced, his supply lines became overstretched, and his army was severely weakened by disease and malnutrition. The harsh Russian winter exacerbated these problems, leading Napoleon to retreat with a significantly reduced force. The Russian victory was not just tactical but strategic, with the harsh climate, vast territory, and Russian resolve playing key roles. When the French invaded, Russia had an army of only 200,000 soldiers, but they successfully harassed Napoleon's retreating forces, contributing to the coalition's efforts to eventually overthrow him.