The way in which expansionism changed the United States' role in the world was it made them more powerful through its capture of new territories and a booming economy.
What was the Monroe Doctrine?
This refers to the American policy of defending countries in the Western Hemisphere from external attacks.
The Monroe Doctrine affected relations between the United States and Latin America as they intervened in Mexico and were victorious which led them to gain new territories.
The way ideas about nationalism affected the way U.S. leaders saw the United States' role in world affairs is that they wanted to protect their interests on both their home soil and abroad which also led to the Monroe Doctrine.
The way the U.S.'s role as an economic power affected its position in the world during the 20th century was that it began to be regarded as a superpower.
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