Why did many Americans oppose the annexation of the Philippines?
There were two main reasons why some Americans did not want to annex the Philippines after the Spanish-American War. One of these reasons was rather noble while the other one was most emphatically not noble.
On the noble side, some Americans like Mark Twain believed that it was simply wrong and un-American to deprive the Filipinos of their independence. After all, here was a country that was acting just like the American colonies had in the 1770s. It wanted to be free from a colonial power that had been oppressing it. And yet here was the United States, a country built on freedom, going over to subdue the Filipinos by force and to annex their country. This seemed completely contrary to all American values and, therefore, these people opposed it.
On the ignoble side, there were many Americans who did not want to annex the Philippines for racial reasons. They worried that, if the US annexed the islands, all of the Filipinos would become American citizens or at least part of the American nation in some way. They did not want a bunch of non-white people being included in the US and they, therefore, wanted to avoid annexing the Philippines.
Some Americans opposed the annexation of the Philippines following the Spanish-American War because they felt that it was not humane. Opponents of annexation formed the American Anti-Imperialist League in 1898. The members of the League, who included Jane Addams, Henry James, and other intellectuals and business leaders, were opposed to annexing the Philippines because they believed that this type of American imperialism violated the principles of American self-government. They used Lincoln's speeches and other foundational American documents such as the Declaration of Independence to argue that conquering the Philippines without the Filipinos' consent violated American principles. Others, such as Mark Twain, the American writer and humorist, fell into this camp, as he felt that imperialism was racist and that it was unjust for white people to colonize countries with non-whites.
There was also an economic argument against annexing the Philippines. Samuel Gompers, head of the American Federation of Labor, and other labor leaders feared that annexation would lead to a flood of Filipino immigrants to the U.S. who would take American jobs. Gompers asked in a speech given in 1898, "If the Philippines are annexed what is to prevent the Chinese, the Negritos and the Malays coming to our country?" He believed that annexation would hurt the American working class by resulting in immigrants who would take away American jobs.