For example, several European states house US nuclear weapons. [1] Japan serves as an outpost against China and North Korea. [2] "Currently South Korean forces would fall under United States control should the war resume. This war time control is planned to revert to South Korea in 2020." [3]
And Vietnam? The south was lead by a series of military governments during the war, which the US was apparently willing to accept. Sure, they pressured for elections, but in the meantime, fighting Communism was more important. [4]
I wouldn't call the US an empire, but they're not exactly a selfless force of protection either.
[1] https://en.wikipedia.org/wiki/Nuclear_sharing
[2] https://en.wikipedia.org/wiki/Japan%E2%80%93United_States_re...
[3] https://en.wikipedia.org/wiki/South_Korea%E2%80%93United_Sta...
[4] https://en.wikipedia.org/wiki/South_Vietnam#1963.E2.80.9373
"According to an annual report titled Allied Contributions to the Common Defense published by the U.S. Department of Defense in 2004, Japan provided direct support of $3.2 billion (about ¥366 billion) and indirect support worth $1.18 billion, offsetting as much as 74.5 percent of the total cost.... [in 2017] It said Japan will pay ¥192 billion in the current fiscal year in direct support. U.S."
https://www.japantimes.co.jp/news/2017/01/31/national/much-j...