The united states had a policy of westward expansion, while mexico had a policy of self protection. What the americans had was actually the idea of manifest destiny. Manifest destiny was the belief that the US had the right to expand westward. Evidence of US expansion is seen with the independence of texas from mexico. The strongest evidence of .
US expansion goals is with the Mexican-American War. Slavery was also a big issue during the 1830's and 40's.
The settlement of Texas played into the united States expansion plans. In the 1830's Texas was still within Mexican borders. Eager for economic growth, the mexican government encouraged US citizens to come and settle. Since mexico banned slavery, most settlers were not happy with this policy and tried to form stronger bonds with the us government than with the mexican government. Arguments anfd fights arose because of this bond, but in 1836 Texas claimed its independence from mexico. .
After texas gained their independence they wanted to join the United States. The US congress voted against texas from joining the Union because they were worried that annexation would anger mexico. Mexico had never officially recognized texas as independent. Congress was concerned that annexation would start war with mexico. Furhtermore, if texas was to become a state, it would be a slave state. Texas enetering the Union would disrupt the balance, giving slave states an advantage in the US House and Senate. Since the US was not ready to annex texas, Texas declared itself a sovereign country and in 1837 President Andrew Jackson recognized Texas as a country.
Texas claimed that New Mexico and California were part of Texas. The boundary with mexico was also disputed. Th US claimed that the Texas border was at the Rio Grande. Mexico said that the border was at the Nueces river. The US tried to settle matters diplomatically so they inexperienced John Slidell.