Some leading causes of the Mexican War were:
* Texan Annexation: Mexico had previously warned that would consider annexation an act of war. When the annexation to place, Mexico actually did not declare war, but broke diplomatic relations.
* Boundary Disputes: Whether Texas was an American state or just a rebellious Mexican Province, the United states continued to maintain the fact that the Rio Grande was Texas's southern border - Mexico insisted that it was actually a river much farther north.
* Pacific Ocean Boundaries: President Polk was determined to expand the country so that its western border became the Pacific Ocean. He did succeed in this.
Cause of the End of the Mexican War: