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How did the end of the American Civil War affect the French campaign in Mexico?

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French Foreign Legion soldiers in uniform with white hats and rifles stand in formation during a Bastille Day parade on the Champs Elysees in Paris. — French Foreign Legion Soldiers of the French Foreign Legion in a parade celebrating Bastille Day in Paris.

The end of the American Civil War in 1865 was a pivotal factor in the collapse of the French intervention in Mexico. With the conclusion of its own internal conflict, the United States began to assert its influence in the region, bringing significant diplomatic pressure on Napoleon III to withdraw French troops, citing the Monroe Doctrine as grounds for their removal.31

Furthermore, the end of the American Civil War freed up U.S. veterans and weapons, which were then utilized to aid the republican forces in their efforts to eject the French-sponsored Emperor Maximilian from power. As the insurgency intensified and the French military presence became increasingly costly and politically unpopular in France, Napoleon III agreed to clear foreign troops from Mexico. The resulting withdrawal of French forces left Maximilian’s imperial government vulnerable, leading to his eventual capture and execution by republican forces in 1867.231