Answer :
The annexation of Texas led to the war with Mexico, with the US victorious in the end. The slave-based cotton production skyrocketed as Texas was used for farming plantations. It also rounded out the borders of the US.
The annexation of Texas helped the United States by adding valuable land to be farmed. This land also helped achieve Manifest Destiny, which was a belief of all Americans the God given right to expand the country from the Atlantic ocean to the Pacific.
