Why did some Americans disagree with U. S. imperialism?

Some Americans disagreed with Imperialism because constantly having the military caused stress and anxiety to the american people and it also felt very strict like the way it was in Britian, hence why we left them for our own freedoms. If you were sitting in school and the U.S. military was walking down the halls, that would cause stress because you would be thinking "oh is there something wrong?" If there were to be a king involved it would just be the same situation that the american people just left, and they wanted something different because that obviously didnt work well.

Explanation:

Imperialism: "a policy of extending a country's power and influence through diplomacy or military force"

"Imperialism is a policy or ideology of extending the rule over peoples and other countries, for extending political and economic access, power and control, through employing hard power especially military force, but also soft power"

"The anti-imperialists opposed the expansion because they believed imperialism violated the credo of republicanism, especially the need for “consent of the governed.” They did not oppose expansion on commercial, constitutional, religious, or humanitarian grounds; rather, they believed that the annexation and administration of third-world tropical areas would mean the abandonment of American ideals of self-government and isolation—ideals expressed in the U.S. Declaration of Independence, George Washington ‘s Farewell Address, and Abraham Lincoln ‘s Gettysburg Address. The Anti-Imperialist League represented an older generation and was rooted in an earlier era; they were defeated in terms of public opinion, the 1900 election, and the actions of Congress and the president because most younger Progressives who were just coming to power supported imperialism"

- American Imperialism | Boundless US History - Lumen Learning

the name of the theory is landmass theory.