What brought American settlers into conflict with the Mexican government?
The issue of slavery.
Settlers went into conflict with the Mexican government because they were planters who brought slaves. Mexico had abolished slavery before and refused this practice. Texas later became independent shortly and joined the USA in 1845.
The settlers from the southern states of the US had agreed to obey Mexican Law and become Mexican citizens in exchange for free land in Texas. The settlers in return were expected to settle and farm the land that was threatened by Indian attacks.
The Settlers refused to obey Mexican Law and brought slaves with them to work their farms and plantations. Instead of yielding to the requests of the Mexican government to obey the law, the Settlers declared themselves to be an independent nation.
The declaration of independence was the final act that brought the American settlers into conflict with the Mexican government.