President Polk told the Senate and House of Representatives that Mexican troops were battling Texas troops near the Nuces and Rio Grande rivers. Texas was their own Republic then, but the battle was also hurting US citizens. President Polk asked them to vote to go to war. On May 13, 1846 they voted to go to war with Mexico.
Abraham Lincoln gave a speech about what we should think about when going to war and who should decide. He talked about how kings send their troops to war and tell them that it is for their own good. Abraham Lincoln said that this time our troops would be going to someone else's country and fighting them. People would get hurt. He did not want the President to act like a king.
General Francisco Mejia made a Proclamation on March 18, 1846 that the United States had violated the rights of Mexico. He said that the US was invading their country and that they were liars. Francisco Mejia said that the place that had been at peace is now going to battle because the US wants the land.