Those Americans who favored expansion and imperialism (the control over another group of people, usually without their consent) relied on the following arguments. First, they saw economic opportunities and benefits to conquering places like Cuba, Hawaii, and the Philippines. The former was useful for naval bases and for growing tropical cash crops. The latter two, while useful for crops too, were seen as important coaling stations, or steam-ship stopping points, between the US and the large market of China.
Second, pro-expansionists argued that the US was racially and religiously superior to the peoples they were conquering. Social Darwinism argued that the Anglo-Saxons, or super-white Northern Europeans who were Protestant and democratic, who allegedly made up the important parts of the US population were morally, spiritually, and intellectually more advanced than the other nations of the world. Thus, they deserved to displace the Spanish (darker racially, Catholic, and less democratic) in ruling over places like the Philippines (Black, allegedly heathen, and allegedly tribal).
Third, pro-expansionists cited competition with Europeans as a reason to expand. We needed to keep with the Europeans, who were experiencing their second wave of imperialism, if we were to become or stay a major world power.
Lastly, the US thought the frontier, the line of Manifest-Destiny style US advancing and thus the mixture of civilization and barbarism, had closed by 1890 since the US had Manifested all the Destiny to be had on the North American continent.
Arguing that the frontier was necessary as an escape valve for those discontented with US civilization and a rugged place where the US could enhance and refine its manly virtues through warfare and battles with nature, these expansionists sought new frontiers overseas in places like the Philippines.
The anti-imperialists like Andrew Carnegie and Mark Twain fought back, forming groups like the Anti-Imperialist League and arguing that ruling over other nations and people who didn’t want the US over them was hypocritical: the US had been a colony once itself. By the 1890s, the language of “self determination” had long been a part of US political conversations, showing the importance of voting and the consent of the governed (John Locke, anyone?).
Anti-imperialists also objected to including more land under the US flag for racial reasons: some objected to adding more non-white people to the US under the racist assumption that they could not be assimilated and would not be capable of participating in US democracy or of living and striving for US ideals and values.
Finally, the anti-imperialists argued that the US had a long tradition of isolationism dating back to the Washington administration and his warning against alliances overseas. This argument saw the US as largely self-sufficient and expansion as opening up a dangerous vulnerability since the US would be closer to competing powers and would necessarily need to expand its military defenses to include ever-larger and far-flung territories.
🎥 Watch: AP US History - American Empire Building