Texas is the only state in the Union that was at one time an independent country. On March 2, 1836, 59 settlers in Texas officially declared independence from Mexico. Mexico didn’t want to lose Texas any more than England wanted to lose the colonies, and the Texas Revolutionary War ensued. The war ended April 21, 1836, but Mexico refused to recognize the independence of the Republic of Texas, and intermittent conflicts between the two states continued into the 1840s.
From the beginning, Texas wanted to become part of the United States but its application was rejected largely because it was a slave-holding region during the build up to the Civil War. Texas finally became the 28th state on December 29, 1845.