Final answer:
The US became an imperialist nation in the late 19th century due to a desire to compete with European empires, economic strength, and the outcome of the Spanish-American War.
Step-by-step explanation:
The United States became an imperialist nation in the late nineteenth century due to several factors. One major factor was the country's desire to compete with the European empires that were expanding their control and influence in other parts of the world. The US saw this as a threat to its economic and political power, and thus began seeking colonies and territories of its own.
Another factor was the economic strength of the US, which surpassed Europe as the major manufacturing power and source of exports. European politicians and businessmen feared being rendered economically obsolete by the US, leading them to focus on territorial acquisition overseas as a counterbalance.
Additionally, the Spanish-American War played a crucial role in the US becoming an imperialist nation. The US gained control of territories such as the Philippines, Guam, and Puerto Rico, positioning itself as a predominant world power in the South Pacific and the Caribbean.