The Catholic Church, conservatives, much of the upper-class and Mexican nobility, and some indigenous communities invited, welcomed and collaborated with the French empire to install Maximilian as Emperor of Mexico.

The intervention was increasingly using up troops and money at a time when the recent Prussian victory over Austria was inclining France to give greater military priority to European affairs.

Facing a mounting combination of domestic political discontent, diplomatic pressure and the growing military threat of Prussia on the borders of Metropolitan France itself, French units in Mexico began to redeploy to Europe in 1866.

Napoleon III was initially not interested, due to the inevitable opposition that the effort would invite from the United States, but the outbreak of the American Civil War provided an opportunity.

Foreign Minister Manuel Doblado invited the commissioners to travel to Orizaba with two thousand of their own troops for a conference while requesting that the rest of the tripartite forces embark from Veracruz.

[18] On 9 April,[19] agreements at Orizaba between the allies broke down, as France made increasingly clear that it intended to invade Mexico and interfere in its government in violation of previous treaties.

Prim consulted with the British and the two agreed to retire their forces after securing that Mexico would devote 80% of custom revenues passing through Veracruz to settle debts with foreign nations.

On 5 May, Mexican forces commanded by Ignacio Zaragoza and Porfirio Díaz won a major victory against the French at the Battle of Puebla while the latter were trying to ascend the hill towards the fortified positions of the city.

[26] Forey reached Orizaba on 24 October 1862, and began planning another siege of Puebla, the defense of which had now passed on to Jesús González Ortega after Zaragoza died of typhoid on 8 September.

On 8 May, François Achille Bazaine and Leonardo Márquez defeated a force of new recruits under former Mexican president Ignacio Comonfort at the Battle of San Lorenzo, when he was coming to reinforce Puebla.

The United States,[31] Honduras, Nicaragua, Costa Rica,[29] El Salvador, Chile, Bolivia, Colombia, Venezuela, Ecuador, Peru, Uruguay, and Argentina all refused to recognize the monarchy and made declarations of support for the Juárez government.

[53] The Imperialists now focused on capturing the north, with Mejía campaigning along the northern Gulf Coast, supported by Charles du Pin's anti-guerrilla corps at Tampico and Édouard Aymard's brigade at San Luis Potosí.

[55] Santiago Vidaurri, the joint governor of Nuevo León and Coahuila, had broken with Juárez in March 1864 over the administration and finances of his state, and even held a referendum on joining the empire.

[62] The defector José López Uraga sent a letter to Díaz hoping to win him over to the imperialist cause, arguing that guerrilla warfare was devastating the country and assuring him that Mexican independence was secure under Maximilian.

[64] Michoacan continued to be a Republican stronghold, serving as a base for Nicolás Régules, Manuel García Pueblita, Carlos Salazar Ruiz, and Vicente Riva Palacio, with the latter being named governor by Arteaga who held supreme command of the regional forces after Díaz's capture.

The operations led by Douay and Manuel Lozada resulted in the defection of the commander of the Republican Central Forces Miguel María de Echegaray, along with General Rómulo Valle.

His successor, Andrew Johnson, never seriously considered overt U.S. intervention, but he did not stop the flow of demobilized, battle-hardened Civil War veterans heading south to volunteer for the Republicans.

[71] In August, as French troops were concentrated in the north under Bazaine, Sinaloa was left protected only by one regiment under Colonel Cotteret in Guaymas, while the surrounding areas were entrusted to Indian allies.

Antonio Rosales was killed in August attempting to retake Álamos,[67] but Ramón Corona pressed upon the imperialists and succeeded in driving French troops from Sinaloa to Mazatlán.

In January 1866, American troops raided Bagdad from Clarksville, a blatant violation of neutrality which resulted in the United States government removing the commander and disciplining those involved.

[83] In Sonora and Sinaloa the French were mostly confined to the ports of Guaymas and Mazatlán, though General Edvard Emile Langberg held positions in the interior with the aid of Opata natives.

Cuautitlán was raided in October, and Chalco de Díaz Covarrubias and Tlalpan were left exposed to Republican incursions in December, while raiders harassed the stream of imperial soldiers and refugees heading to Veracruz.

The Imperialist commander Ortiz de la Peña retreated to Cuernavaca after a defeat at Ixtla, and Régules and Vicente Riva Palacio occupied the Lerma Valley.

The country was divided into three military districts: the western, comprising the provinces north of Colima, including Durango and Chihuahua; the eastern, stretching from Aguascalientes and Tampico northward; and the central, embracing all the vast remainder to Chiapas.

Miramón was placed at the head of the infantry, of which Castillo and Casanova received a division each, Méndez assumed command of the reserve brigade, in which López served as colonel, Mejía became chief of the cavalry, Reyes of engineers, and Arellano of the artillery.

[103] In the first council of war held on 22 February, it was agreed to fight the Republicans before their combined forces became too strong, but ultimately this strategy, which historian Hubert Howe Bancroft suggested could have achieved victory, was rejected on the advice of Márquez.

[113] Many European monarchs[113] and other prominent figures (including Victor Hugo and Giuseppe Garibaldi)[citation needed] pleaded Juárez for Maximilian's life to be spared, but he refused to commute the sentence.

[citation needed] As early as 1859, U.S. and Mexican efforts to ratify the McLane–Ocampo Treaty had failed in the divided United States Senate, where tensions were high between the North and the South over slavery.

We should have thus been relieved from the obligation of resisting, even by force, should this become necessary, any attempt of these governments to deprive our neighboring Republic of portions of her territory, a duty from which we could not shrink without abandoning the traditional and established policy of the American people.

[121] In 1866 General Philip Sheridan was in charge of transferring additional supplies and weapons to the Liberal army, including some 30,000 rifles directly from the Baton Rouge Arsenal in Louisiana.