What event is widely regarded as the beginning of Napoleon Bonaparte's decline in power?

The disastrous invasion of Russia is widely regarded as the pivotal moment marking the beginning of Napoleon Bonaparte's decline in power. In 1812, Napoleon launched an ambitious military campaign into Russia, promising a quick and decisive victory. However, the campaign turned into a catastrophic retreat as the Russian forces employed a scorched earth policy, destroying supplies and resources that could have supported Napoleon's army. The harsh winter conditions further decimated his troops, leading to enormous losses; of the approximately 600,000 soldiers who initially marched into Russia, only a fraction made it back.

This failed campaign not only weakened his military might but also severely diminished his reputation both domestically and across Europe. The losses faced in Russia emboldened other European nations to rise against him, as it demonstrated that he was no longer invincible. This event set off a chain reaction that led to his eventual defeat and the coalition forces' resurgence, ushering in a significant decline in his power and influence.