The French intervention in Mexico (Spanish: Segunda Intervención Francesa en México), also known as the Maximilian Affair, War of the French Intervention, and the Franco-Mexican War, is an invasion of Mexico by the Second French Empire, supported in the beginning by Great Britain and Spain.

It follows President Benito Juárez's suspension of interest payments to foreign countries on 17 July 1861, which angers Mexico's major creditors: Spain, France and Britain.Napoleon III of France is the instigator, justifying military intervention by claiming a broad foreign policy of commitment to free trade.

For him, a friendly government in Mexico would ensure European access to Latin American markets.

Napoleon also wants the silver that could be mined in Mexico to finance his empire.

Napoleon builds a coalition with Spain and Britain while the U.S. is engaged in a full-scale civil war.

The U.S. protests but can do nothing until 1865.

The three European powers sign the Treaty of London on October 31, to unite their efforts to receive payments from Mexico.

On December 8, the Spanish fleet and troops arrive at Mexico's main port, Veracruz.

When the British and Spanish discover, however, that France plans to seize all of Mexico, they quickly withdraw.The subsequent French invasion results in the Second Mexican Empire, which is supported by the Roman Catholic clergy, many conservative elements of the upper class, and some indigenous communities; the presidential terms of Benito Juárez (1858–71) are interrupted by the rule of the Habsburg monarchy in Mexico (1864–67).

Conservatives, and many in the Mexican nobility, try to revive the monarchical form of government when they help to bring to Mexico an archduke from the Royal House of Austria, Maximilian Ferdinand, or Maximilian I of Mexico (who marries Charlotte of Belgium, also known as Carlota of Mexico), with the military support of France.

France has various interests in this Mexican affair, such as seeking reconciliation with Austria, which had been defeated during the Franco-Austrian War of 1859, counterbalancing the growing American Protestant power by developing a powerful Catholic neighboring empire, and exploiting the rich mines in the northwest of the country.