Why did James Polk started the Mexican American war?

Answer 1

To gain approval from Congress in the form of a Declaration of War usually requires much more than bad blood or feuding, spilled blood is a better excuse to vote in favor of going to War. In any case when troops are placed in harms way it becomes almost inevitable that hostilities in some form will happen. Mexico insisted that the Neuces River was the traditional border for the Mexican State of Tejas and the Texians favored the Rio Grande del Norte as the border. The spaces between the two rivers was treated as a "no man's land" for almost a decade. The Thornton Affair was simply the clash (Casus belli) that spilled enough blood to justify a reluctant Congress to declare War on Mexico.

Answer 2

Polk wanted something to happen in order to get public support for a war against Mexico. This is why when American soldiers crossed the border into Mexico and were attacked by Mexicans, Polk said that "American blood had been spilled on American soil". Even though this statement was false(the soldiers were in Mexico) it was the event that now made war viable because the public would support a war to defend its borders. Polk like many presidents wanted to expand United States borders.

Answer 3

It would be very difficult to sell to the public something on the lines of "yes, we want Mexico's land so that we can expand westward at all costs; it may mean 20,000 American casualties, do you agree?". The winning formula since then (remember Iraq?) has been a red flag operation where "Americans have been killed without provocation" justifies any military confrontation. Then invade.

Answer 4

He wanted to annex Texas into America and got into a dispute with Mexico over it.

Answer 5

To provide Manifest Destiny.