Causes of the War

Texas entered the Union as a slave state in December 1845.

The question was the border with Mexico.  Where was it???

  • The Rio Grande?
  • The Nueces River ?


  • General Zachary Taylor’s mission-  President Polk sent General Taylor and his soldiers to occupy the contested land between the two rivers between Texas and Mexico.  He was instructed to simply occupy the land that the US believed was rightfully theirs based on the Treaty signed by Santa Anna.
    • The inevitable conflict began in May 1846 when Mexican forces clashed with American soldiers which killed eleven Americans.
    • Polk had already prepared his war declaration and rushed it to Congress for approval on May 11, 1846.

texas dispute

  • Democrat response to war with Mexico- supported the war with Mexico – especially those Democrats from the south
  • Whig response to war with Mexico- most Whigs opposed the war with Mexico – especially those from the North because they feared Polk would also plot to take New Mexico and California.  They feared this large territory would boost the southern slave states’ power in Congress


  • Whigs not block the declaration of war by Congress- because they knew this was a popular war and they feared being on the wrong side of a popular war.  They remembered the collapse of the Federalists who had opposed the popular War of 1812