The Outbreak of War

• USA's annexation of Texas angered Mexico, which still claimed sovereignty over Texas
• Barely concealed desire of Polk's California and New Mexico didn't help US-Mexico tension / relations
• Efforts to reach agreement undermined by Mexican situation
• Mexican government came and went rapidly that it was difficult for USA to know with whom to deal with.
• In 1845, Polk sent US troops into the disputed border area North of Rio Grande River, hoping to provoke an incident that would result in war which would then lead to US annexation of California and New Mexico
• May 1846, Mexican troops duly ambushed a party of US troops in the disputed area, killing / wounding 16 men
• Polk claimed they "shed American blood on American soil" and asked Congress to declare war - they agreed
• South and West supported War but the North saw it as Southern war of aggression.