What led most directly to Napoleon bonapartes?

He was already losing popularity during the 1860s, especially after his attempt to control Mexico failed. Prussia, which was trying to unify Germany under their own rule, picked a fight with France, sparking the Franco-Prussian War. At the climactic battle of Sedan, the Prussian Army soundly defeated the French Army, and Napoleon himself was captured.

With Napoleon captured, his government immediately collapsed and he was removed from power. A new republican government formed and tried to continue the war. The Germans besieged Paris, and after a few months, captured it, effectively ending the war. Napoleon was eventually freed and decided to go into exile in England, where he died a couple years later.