Why was Mexican was condsidered controversial?

The Mexican War (1846-1848) was considered controversial due to its aggressive expansionist motives, as many viewed it as a means for the United States to expand its territory at the expense of Mexico. The conflict raised ethical concerns about Imperialism and the treatment of Mexican citizens, as well as fears of slavery's expansion into new territories. Additionally, the war deepened divisions within the U.S., leading to debates over the morality of the conflict and its implications for national identity and foreign policy.