The main strategic objectives of the United States in the Mexican–American War were to secure the disputed Texas territory, obtain the Mexican territories of California and New Mexico, and establish the Rio Grande as the southern border of Texas. Control of California was particularly desirable for its ports, which would allow for expanded trade in the Pacific, and the anticipated economic benefits, which were later confirmed by the California Gold Rush. Additionally, the US sought to demonstrate its military might and solidify its position as a dominant power in North America.

The Mexican–American War had a profound influence on US domestic politics, exacerbating sectional tensions over the issue of slavery. The acquisition of new territories raised pressing questions about whether these territories would permit slavery, leading to heated debates in Congress. This issue was temporarily addressed by the Compromise of 1850, which attempted to satisfy both free and slave states. However, the divisive politics around these territories contributed to the mounting discord that would eventually lead to the American Civil War.

Naval power played a significant role in the Mexican–American War, particularly for the United States, which used its naval forces to blockade Mexican ports and cut off supply lines. The US Navy was instrumental in the capture of key coastal cities like Veracruz, which served as a gateway for further military campaigns into the Mexican heartland. The US also leveraged its naval superiority to secure the California coast and claim San Francisco Bay, contributing significantly to the successful annexation of the western territories.

The Mexican–American War set several precedents for future American foreign policy. It was the first US war fought primarily on foreign soil and the first in which American troops occupied a foreign capital. The war established a pattern of using military force to achieve foreign policy goals, specifically territorial expansion. It also set a legal and diplomatic precedent through the Treaty of Guadalupe Hidalgo, which would influence later US treaties and acquisitions. Furthermore, the war demonstrated the effectiveness of promoting domestic ideological concepts, such as Manifest Destiny, to garner public support for international interventions.

The US government justified the annexation of Texas through the ideology of Manifest Destiny, which held that the expansion of the US across the American continent was both justified and inevitable. The annexation was portrayed as a natural extension of American liberty and democracy. Additionally, the US government argued that Texas had established itself as an independent republic with the right to seek annexation following its successful secession from Mexico in 1836. The US also cited the desire of many Texans to join the Union and the potential security threat posed by foreign powers establishing influence in Texas.