A. Political independence from Europe
"Imperialist" refers to the will to rule over a vast territory ( the empire).
The problem with territory is that it is limited. So if multiple entities want to rule over vast territories, they will end up competing with each other over any new territories that still aren't dominated by others. Even if those new territories won't be (immediately) incorporated into the empires, each of the empire would want to exercise power or influence over them.
This leads to conflicts, and rivalry, and was a reason for the tension between the European powers at the onset of WW1. WW1 was in a way a possibility for each of the powers to gain advantage by showing that they're stronger to the others. They believed that the winning power could then claim power and influence over new lands.
Answer: in the 2nd part of the 19th century USA were convinced of their racial superiority (also thanks to social Darwinism, biologization of social sciences and biological determinism that existed in Europe but also in the South America) and felt their obligation to reform the "inferior races" of the region. So Washington bureaucrats attempted to reshape countries such as Cuba into model versions of their own republic. That is what happened in times of Theodor Roosevelt´s bureaucracy. But before that "conquest" of the South was something which was an affair of adventurers and entrepreneurs with frequently economic interests (William Wheelwright in Chile, Stephens in Central America).
Explanation: Presidents like Thomas Jefferson and John Adams viewed Spanish possessions, including Florida, today´s Texas, and Cuba, as regions that should and would be incorporated into the United
States. Racial aspect was always present ...many people in the USA saw themselves as part of a superior Anglo-Saxon race.
They sent troops over the the country that is decaring war
