Should the U.S. have tried to be an imperial power or should the U.S. have stayed out of world affairs between 1890 and 1919?
Why did the U.S. become an imperial power in the late 19th century?
The US became an imperial power because the older imperial powers were in decline. The Spanish-American War (1898) is the clearest example of the United States' transition from a national to imperial power, largely due to the long decline of Spain, whose influence in the New World had been slowly waning for centuries. At this time, the US began expanding overseas for the first time, securing islands in the Caribbean and the Philippines in the Far East. Not only had the US fulfilled the original projections of the Monroe Doctrine, but they had gone beyond it in expanding and extending their influence. Although the nominal excuse for the United States to join in World War I was the outrage at the sinking of the Lusitania, and the damage unrestricted submarine warfare would do to US shipping (which were supplying the enemies of Germany) the more important reason for embroiling the US in that cataclysmic European conflict was due to the Zimmerman Telegram -- that Germany would support Mexico in invading restoring its territories lost to the US and Texas in the 1840's. The threat that the US felt from not only Germany but other European powers influencing the Western Hemisphere forced the US to fight, for defensive purposes. Having landed on the winning side after World War I, the US influence around the world grew as European influence around the world shrank. Postwar, US got "sucked into" the power vacuum caused by the disintegration of Europe, which until that time, had proudly run the planet.
The second part of your question is much easier to answer. The US became an imperial power for the following reasons:
- For economic power. The US wanted to get captive markets and guaranteed sources of various things. Colonies give a country both of those things.
- For military power -- the US wanted naval bases around the world (Alfred Thayer Mahan's theory about the importance of naval power affected this).
- For the purposes of "the White Man's Burden" -- they felt they were superior to everyone who was not white and Protestant.
Should they have done this? This is totally subjective. In those days, every strong country was taking an empire. If the US had not, it probably would have been left behind and might have been seriously weakened. So it may seem immoral to us now, but it probably made a lot of sense back then in terms of keeping the US strong.
USA did exercise control over some countries at the turn of twentieth century, but that was not much of an imperial power. Twentieth century is marked more for end of imperial power all over the world, rather than for creating new imperialist countries or for strengthening the existing ones. I believe it would have been a futile exercise, and perhaps a big mistake for USA to try to become a big imperialistic power beginning from 1890 onwards.
Technological, economical, social, and political situation as it existed then and developed subsequently, made imperialism a loosing proposition. Today, imperialism is dead, and it is quite unlikely that USA could have become a strong imperialistic power against the general march of world progress.
Staying out of world affairs during the period between 1890 and 1919, also would not have been wise considering the world trend. The world is becoming more interconnected - we call this phenomenon globalization. No country in that period or after that can expect to serve its interest better by remaining insulated from the rest of the world.