Manifest Destiny exerted a significant influence on American foreign policy during the 19th century. The ideology's core belief in American territorial expansion led to several notable events and actions. Let's explore three key examples: the annexation of Texas, the Mexican-American War, and the acquisition of territories like California, New Mexico, and Arizona.

1. Annexation of Texas

One prominent manifestation of expansionism was the annexation of Texas in 1845. At the time, Texas was an independent republic, having successfully gained independence from Mexico in 1836. The United States, driven by the idea of Manifest Destiny, sought to incorporate Texas into its borders, leading to its official inclusion as a state. The annexation of Texas heightened tensions with Mexico, setting the stage for the Mexican-American War.

2. Mexican-American War

The Mexican-American War (1846-1848) was a pivotal conflict rooted in territorial aspirations. The United States, spurred by the belief that it was destined to control the entire continent, engaged in a military campaign against Mexico. The war resulted in significant territorial gains for the United States, including the cession of territories such as California, New Mexico, Nevada, Utah, Arizona, and parts of Colorado and Wyoming. These acquisitions further fueled the idea of Manifest Destiny and solidified American control over vast western territories.

3. Acquisition of California, New Mexico, and Arizona

The acquisition of California, New Mexico, and Arizona was a crucial step in the westward expansion of the United States. The California Gold Rush in 1848 created a surge of migration to the region, leading to an increased push for American control. As a result, the Treaty of Guadalupe Hidalgo, signed in 1848, ended the Mexican-American War and granted the United States vast territories, including California, New Mexico, and parts of Arizona, Nevada, Utah, and Colorado.

In conclusion, expansionism, driven by the notion of Manifest Destiny, influenced American foreign policy during the 19th century and played a significant role in shaping territorial acquisitions. The annexation of Texas, the Mexican-American War, and the acquisition of territories like California, New Mexico, and Arizona all attest to the powerful impact of this ideology on the nation's expansionist ambitions.