A navy needs ports and the ability to quickly deploy therefore the US needs to have colonies to set up those ports.
Alfred Mahan wrote the Influence of Sea Power Upon History as well as other variations which outlined the importance of a navy and the need for colonies to support the navy. Mahan argued that to truly protect the trade interests and industrial power of the US, they needed to create a strong navy to protect shipping. However, only having access to ports on the coastlines of the US prevented quick deployment and close range protection of Asia trade. Therefore he argued the US needed to get colonies so they could create naval bases on the colonies. The US would get their first colonies in 1898 (just eight years after the release of his book) from the Spanish-American War.