Why was the territory of Texas annexed by the United States?

A)
Spain forced Mexico to allow annexation to happen after years of conflict.

B)
Texas was added to the United States as a result of the Mexican-American
War.

C.
In 1845, the Republic of Texas voluntarily asked to be admitted to the
United States

D)
Texas was annexed at the same time as California making the increase in
sizable for the United States.