What were the issues between the US and Mexico before they went to war?

The main issue between the US and Mexico was the American Southwest and whom it should belong to. Mexico had held this land since their separation from the Spanish Empire, and the US wanted to buy it for $30 million, but Mexico staunchly refused to sell. Also, US citizens (including former US Congressman What issues existed between the US and Mexico before the Mexican war? David Crockett) had fought and died fighting for the Republic of Texas, and after ten years Texas had recently become a US state. The disputed Tex-Mex What issues existed between the US and Mexico before the Mexican war? border then became an issue for the US. Also, in the opinion of this contributor, religion may have been an issue. Christians were no longer fighting

The US wanted Texas. So they made a fort there and the Mexican people were like no! So they attacked the fort and killed ALL of the American people in the fort (excluding slaves, women, and children. Only soldiers.)