Quoc: The Texas annexation was the 1845 incorporation of the Republic of Texas into the United States of America, which was admitted to the Union as the 28th state on December 29, 1845.

When did texas annexed into the united states?
HW Chung: OK, some thoughts:
The relevant sentence in the passage is: The Texas annexation was the 1845 incorporation of the Republic of Texas into the United States of America, which was admitted to the Union as the 28th state on December 29, 1845. The answer is 1845.