Isolationists argued that the acquisition of new territory would increase the risk of war and would also lead to increased government spending. They also believed that the United States had no responsibility to acquire new territory and that doing so would be a violation of the principles of self-determination.
Despite the opposition of isolationists, the United States did annex a number of territories in the late nineteenth century, including the Hawaiian Islands, Puerto Rico, and the Philippines. These annexations were often justified on the grounds of national security or economic interests.