What is annexation of Mexican territory an example of?

The annexation of Mexican territory is an example of Imperialism, where a nation expands its control over foreign lands, often through military force or coercive treaties. This can also be viewed as a manifestation of Manifest Destiny, a 19th-century belief in the United States that it was destined to expand across the North American continent. The annexation led to significant geopolitical changes and conflicts, particularly evident in the Mexican-American War.