The
Mier Expedition was an offshoot of the
Somervell Expedition, an unsuccessful military operation launched in November 1842 by a
Texian militia against
Mexican border settlements. It included a major battle at
Ciudad Mier on December 26 and 27, 1842 which ended with a costly Mexican victory. The attack was partly in hopes of financial gain and partly in retaliation for the
Dawson Massacre (as named by Texans) earlier that year, in which thirty-six Texas militia were killed by the
Mexican Army. Both conflicts were part of continuing efforts by each side to control the land between the
Rio Grande and
Nueces River. Texas believed that this territory had been ceded to the Republic in the
Treaties of Velasco, by which they gained independence; but Mexico did not agree.