Looking for “American imperialism” on Youtube, I was surprised by the large number of videos. Where to begin? What to choose? Well, lets start with trying to understand what is meant by the word “imperialism” (Wikipedia). Imperialism involves rule by a foreign government with or without colonization. The point of ruling a land area is to extract from it some advantage, as through taxation or through some business operation. A notorious example of such a business operation was that of Leopold II of Belgium: “Leopold extracted a fortune from the Congo; initially by the collection of ivory and after a rise in the price of rubber in the 1890s, by forced labour from the native population to harvest and process rubber. Under his regime millions of the Congolese people died. Modern estimates range from one million to fifteen million, with a consensus growing around 10 million.”
Imperialism can proceed by incorporating adjacent or non-adjacent territory under the rule of a State. In the case of the United States, though there were objections to the land-grabs from the Mexicans in the Mexican- American War (1846-1848). [“Acting on his convictions, Henry David Thoreau was jailed for his refusal to pay taxes to support the war, and penned his famous essay Civil Disobedience.”]
This business of expanding the territory of the United States through the acquisition of adjacent territory was not called “imperialism,” until the U.S. got into the business of acquiring rule over non-adjacent territories through the Spanish-American War in 1898. This war started as a war for the liberation of Cuba and the Philippines from Spanish imperialism, but the United States refused to give either Cuba (and Puerto Rico) or the Philippines independence. This led to the Philippine-American War (1899-1902), resulting in 1/4 million dead Filipinos.
In 1898, in opposition to the annexation of the Philippines, there was formed in the United States the American Anti-Imperialist League (Wikipedia), of which Mark Twain, from 1901, was vice-president.
Stephen Kinzer just published a book about the start of American imperialism: THE TRUE FLAG: Theodore Roosevelt, Mark Twain, and the Birth of American Empire, 2017. Below is a talk which Kinzer gave on the book: