How would you describe Polk’s stated and unstated reasons for going to war?

President Polk's unstated reason for declaring war on Mexico was not legitimate, in my opinion, but his stated reason was.

Polk believed America should expand coast to coast and wanted Mexican land in present-day Texas, New Mexico, Arizona, California, etc. However, Mexico refused to negotiate the sell of the land to the U.S. and Polk believed the only way to get it was to go to war with Mexico. But he didn't have an official reason to start a war with Mexico.

Polk then sent U.S. troops to Texas, he said to protect the American interests and citizens there, but I believe he sent troops there to provoke an altercation with Mexico and then he would have an official reason to declare war on Mexico. That's why I believe his unstated reasons weren't legitimate.

Then Mexican troops did attack and kill U.S. troops and citizens in Texas near the Rio Grande River. Polk then went to Congress and asked for a declaration of war against Mexico because they attacked U.S. troops/citizens on American soil, which was a legitimate reason.

edit:

I forgot to add that after Texas became a U.S. state there was still a dispute with Mexico over where the border between Texas and Mexico actually was. Mexico claimed it was along the Nueces River but the Texans claimed it was about 50 miles further south along the Rio Grande River, which is the official border today. That's why President Polk sent troops to the Rio Grande, he knew it would upset Mexico and probably provoke a military response.

I take it you are referring to Leonidas K Polk?

I suppose it is odd for a bishop to double as a Major-General; but his country (well, his state) was at war, and he thought it was his duty to play his part.

Which is true for the vast majority of all ths men who have ever gone to war. They didn't start it, but they thought it was right to answer when their country called.