Henry Lane Wilson in the context of United States Ambassador to Mexico

The Ten Tragic Days (Spanish: La Decena Trágica) is the name given to the multi-day coup d'état during the Mexican Revolution in Mexico City. It was staged by opponents of Francisco I. Madero, the democratically elected president of Mexico, between 9–19 February 1913. The coup instigated a second phase of the Mexican Revolution, after dictator Porfirio Díaz had been ousted and replaced in elections by Francisco I. Madero. The coup was carried out by general Victoriano Huerta and supporters of the old regime, with support from the United States, especially U.S. ambassador Henry Lane Wilson.

In the ten days of violence, the aim was to "create the illusion of chaos necessary to induce Madero to step down" from the presidency. Rebels led by General Félix Díaz, nephew of ex-president Porfirio Díaz, and General Bernardo Reyes escaped from jail and rallied forces to overthrow President Francisco I. Madero. The coup was strongly supported by U.S. Ambassador to Mexico, Henry Lane Wilson, who was implacably opposed to Madero. Madero had retained the Mexican Federal Army after rebels had forced the resignation of President Porfirio Díaz. The head of the Mexican Federal Army, General Victoriano Huerta, ostensibly the defender of the Madero government, defected to the rebels, who sought the return of the old political order. On 18 February the sitting president and vice president were captured by rebel General Aureliano Blanquet, effectively ending Madero's presidency. On 19 February, a dispute between General Díaz and General Huerta about who should head the provisional government was resolved by Ambassador Wilson mediating between the two in an in-person meeting at the U.S. embassy. They formalized an agreement known as the Pact of the Embassy.

The Pact of the Embassy, also known as the Pact of the Ciudadela, is a February 19, 1913, agreement brokered by U.S. Ambassador to Mexico Henry Lane Wilson during the coup to oust democratically-elected Mexican President Francisco I. Madero. Wilson had opposed Madero's government from its beginning and had done everything he could to undermine it. In a period of the Mexican Revolution known as the Ten Tragic Days ("Decena Trágica"), forces opposed to Madero had bombarded the center of Mexico City with artillery fire, with the loss of civilian life and destruction of buildings. Madero's chief military man, General Victoriano Huerta, put up a desultory effort to combat the rebels, which some see as a "phony war."

Ambassador Wilson brought together the two rival generals whose forces were responsible for the destruction, Huerta, head of the Mexican Federal Army, in whom Madero had misplaced his trust, and General Félix Díaz, nephew of former Mexican President Porfirio Díaz. Wilson aimed to broker an agreement to end the bloody violence, which several historians see as the pretext for the ouster of Madero. Huerta changed his allegiance and was now plotting to oust Madero. The pact terms were that Díaz would recognize Huerta as provisional president of Mexico, with Huerta allowing Díaz to name Huerta's cabinet, presumably with his supporters. They further agreed that rather than holding quick elections, they would delay them, and Huerta would support Díaz's candidacy.