The correct answer is A) Texas was an independent nation.
It was difficult for the United States to annex Texas because Texas was an independent nation.
By the time the United States wanted to annex Texas, Texas was an independent nation. They did not depend more from Mexico. Texas got its independence from Mexico in 1836.
As they were already independent, Texans were not interested in joining the United States. They did not see a valid reason why because one way or the other, they knew how to prosper themselves. And some Northern states did not want the annexation of Texas because it would be another slavery state for the Confederates. Texas was finally annexed to the US on December 29, 1845.
