There were at least two major factors that motivated US policy towards Latin America during this time.
First, there was a desire for economic gain. The US wanted to use Latin America as its own economic "hinterland." Therefore, it tried to keep close control over such countries as Cuba.
Second, there was a desire to keep Latin America as the United States' own strategic sphere of influence. This involved being sure that European countries could not come in and have a great deal of influence in the region. This was manifested in the Roosevelt Corollary to the Monroe Doctrine and in actions that were taken as a result of that policy.
Latin americas immigration into unitedstates in the 1920s vs now