Mexican War of Independence
Iturbide's assignment to the Oaxaca expedition coincided with a successful military coup in Spain against the monarchy of Ferdinand VII. The coup leaders, part of an expeditionary force assembled to suppress the independence movements in the Americas, had turned against the monarchy. They compelled the reluctant Ferdinand to reinstate the liberal Spanish Constitution of 1812 that created a constitutional monarchy. When news of the liberal charter reached Mexico, Iturbide perceived it both as a threat to the status quo and a catalyst to rouse the criollos to gain control of Mexico. Independence was achieved when conservative Royalist forces in the colonies chose to rise up against the liberal regime in Spain; it was an about-face compared to their previous opposition to the peasant insurgency. After an initial clash with Guerrero's forces, Iturbide assumed command of the royal army. At Iguala, he allied his formerly royalist force with Guerrero’s radical insurgents to discuss the renewed struggle for independence.
Japan–Mexico relations
In 1874 (fifty-three years after Mexico declared independence from Spain in 1821), a Mexican scientific delegation headed by Francisco Díaz Covarrubias arrived in Japan to witness the transit of the planet Venus through a solar disc. Although the scientific delegation did not have much success, this mission did allow for formal diplomatic relations to begin between the two nations. In 1888 Foreign Ministers Matías Romero and Munemitsu Mutsu signed a Treaty of Amity, Commerce, and Navigation; which was to be Japan's first "equal" treaty with a foreign nation and thus formally established diplomatic relations between the two nations.