1. Manifest Destiny: The belief in the inherent right and duty of the United States to expand its territory across North America.
2.Economic Expansion: The desire for economic growth, natural resources, and access to new markets led to the expansion overseas to establish colonies and trade route.
3. Military Power: The growth of the U.S military strength provided the means to protect its interests abroad.
4. Cultural and Missionary Zeal: The U.S. saw itself as a benevolent force and believed it had a duty to spread its democratic ideals, Protestantism and civilizing influence to the rest of the world.
5. Imperial Competition: The United State wanted to maintain its power status and influence in a world dominated by European imperial powers, such as Britain, France and Russia.
6. Geopolitics: Acquiring overseas territories would provide strategic military bases, enhance national security and give the U.S. access to important trade routes.
7. Social Reform and Urbanization: Some believed that overseas would give opportunity to surplus population, reduce unemployment and promote social reforms at home.
8. Racism: The prevailing view of racial hierarchies and the belief in the superiority of the white race made it acceptable for the U.S. to dominate territories with indigenous population.
9. Technological Advancements: The development of steamships, telegraph and other technologies made overseas expansion more feasible.
10. National Prestige: Some Americans believe that expanding overseas would enhance the nation's international prestige and recognition as a major world power.