Which nation exercised the greatest foreign influence in the american southwest?

The nation that exercised the greatest foreign influence in the American Southwest historically was Spain. Spanish explorers and missionaries were the first Europeans to extensively explore and colonize the region, beginning in the 16th century. They established settlements, missions, and forts, leaving a significant cultural, architectural, and linguistic legacy that can still be seen today in the place names, architecture, and demographics.

During the period of Spanish colonization, the region was part of the Spanish Empire, known as New Spain, which included territories across much of what is now the southwestern United States, Mexico, and other parts of North and Central America. In 1821, Mexico gained independence from Spain, and the Southwest became part of Mexico until the mid-19th century when the United States acquired the territory through various means, including the Mexican-American War and the Gadsden Purchase.