Mexican Cession Mexican Cession, with considerable local autonomy punctuated by several revolts and few troops sent from central Mexico, in the period from 1821–22 after independence from Spain up through 1846 when U.S. military forces seized control of California and New Mexico on the outbreak of the Mexican–American War. The northern boundary of the 42nd parallel north was set by the Adams–Onís Treaty signed by the United States and Spain in 1821 and ratified by Mexico in 1831. The eastern boundary of the Mexican Cession was the Texas claim at the Rio Grande and extending north from the headwaters of the Jojo
First Mexican Empire First Mexican Empire The Mexican Empire (, ) was a short lived monarchy, and the first independent post-colonial imperial state in Mexico. It was the only former colony of the Spanish Empire to establish a monarchy after independence. Together with the Brazilian Empire, it was one of two European-style empires in the Americas. The Mexican Empire lasted two years. It existed from the signing of the Treaty of Córdoba and the declaration of Independence of the Mexican Empire in September 1821 until the emperor's abdication in March 1823 when the Provisional Government took power and the First Mexican Republic was