The answer is slavery. The Republicans were anti-slavery, while the democratic south was pro slavery. Eventually that, and a couple of other things, led to the Civil War.
Sorry if this was a bit late, Brainly had just recommended this question for me to answer, but I hope this helps!
President Polk wrote this address to Congress on May 11, 1846 to the Senate and the House of Representatives:
The existing state of the relations between the United States and Mexico renders it proper that I should bring the subject to the consideration of Congress. In my message at the commencement of your present session, the state of these relations, the causes which led to the suspension of diplomatic intercourse between the two countries in March, 1845, and the long-continued and unredressed wrongs and injuries committed by the Mexican Government on citizens of the United States in their persons and property were briefly set forth.
As the facts and opinions which were then laid before you were carefully considered, I can not better express my present convictions of the condition of affairs up to that time than by referring you to that communication.
<span>Jefferson’s basic elements of the argument for separation were
lack of respect. Furthermore, he framed the arguments in a way that shows that the
violation of economic and political rights that the Colonists have had to
suffer were the result of a lack of respect. Jefferson is empathizes with the
British government in how they have refused to "assent" to the basic
principles of dignity and decency that would eventually enable a successful
relationship and partnership to develop.</span>
You'll need to be recognized by the people that live there, as well you'll need to make sure you declare your independence be ready for big financial problems
