Final answer:
The Mexican-American War led to considerable territorial gains for the United States but also caused increased internal tensions over land, political power, and slavery, as well as damaged relations with Latin American countries due to perceived American aggression.
Step-by-step explanation:
Effects of the Mexican-American War on the United States
The results of the Mexican-American War had both beneficial and detrimental effects on the United States, impacting specific groups and regions within the country. On one hand, the war was a significant military victory, leading to the gain of the Mexican Cession, and it showcased the strength of the U.S. military training, as evidenced by military successes like the conquest of 'the halls of Montezuma.' This gain spurred debates in the North against slavery and mobilized many who had not previously been engaged with the abolitionist movement.
On the other hand, the war exacerbated tensions between various groups within the United States. The acquisition of new territories increased hostilities between Americans and Mexicans in Texas and California, with Hispanics being dispossessed and politically disenfranchised. Native Americans saw increased aggression and conflict as settlers pushed westward. Moreover, the war upset the delicate balance of slave and free states, threatening the political truce over slavery following the Missouri Compromise, and ignited further debate with the introduction of the Wilmot Proviso.
Externally, the war also harmed U.S. relations in Latin America, intensifying 'Yankeephobia' due to perceptions of American greed and provocation. In the domestic realm, the war set the stage for future conflict, contributing to the sectional crisis that would eventually erupt into the Civil War. The Treaty of Guadalupe Hidalgo and the resulting territorial acquisitions raised questions about the expansion of slavery, which the Compromise of 1850 and other attempts at conciliation failed to durably resolve, culminating in further division and ultimately secession.