What was the major reason for napoleons defeat during his invasion of Russia in 1812?

The major reason for Napoleon's defeat during his invasion of Russia in 1812 was the harsh Russian winter, which his troops were ill-prepared to endure. Additionally, the scorched earth tactics employed by the Russians left the French army without adequate supplies and shelter. These factors, combined with the relentless Russian military resistance, led to massive losses and ultimately forced Napoleon to retreat, resulting in a catastrophic decline in his army's strength.