 Complete the following phrase:  Most of the area had been the Mexican territory of Alta California, while a southeastern strip on the Rio Grande had been part of Santa Fe de Nuevo México, most of whose area and population were east of the Rio Grande on land that had been claimed by the Republic of Texas since 1835, but never controlled or even approached aside from the Texan Santa Fe Expedition. Mexico controlled the territory later known as the Mexican Cession, with considerable local autonomy punctuated by several revolts and few troops sent from central Mexico, in the period from 182122 after 