The ideas expressed in Manifest Destiny were clearly evident in our policies regarding Texas. Manifest Destiny refers to our desire and expectation to expand from the Atlantic Ocean to the Pacific Ocean.
Once Texas became independent, there were people who wanted to annex it immediately. The only thing holding us back from annexing Texas was the issue involving slavery. If this issue could have been resolved, Texas would have immediately joined the United States upon becoming independent. It took nine years for Texas to join the United States, but there was never any real question if that would happen. It was more a question of when it would happen.
Once Texas became a part of the United States, we wanted to expand into land controlled by Mexico in what is now the southwest part of the United States. When a border dispute arose with Mexico over the boundary with Texas, we moved our troops into the disputed territory. Once our troops were attacked, we went to war against Mexico with the goal of adding more land to the United States. This was accomplished with our victory in the Mexican-American War. Not only was our border between Texas and Mexico set at the Rio Grande River, we gained much of what is now the southwest region of our country.