Did the Monroe Doctrine prevent against certain European influences against Latin America, as it prevented European countries from colonizing them for a long period of time?
At the time it was announced, the Monroe Doctrine was not particularly meaningful, as the United States lacked the capability to prevent European powers from interfering in the affairs of the newly-independent South American states. In any case, Monroe's primary concern were Russian and English claims on what would become the Oregon Territory in the modern-day American Northwest. The reason the Monroe Doctrine was effective at the time in South America, however, was that the British government also wanted to keep Spain from interfering in the region, and their navy was capable of enforcing their wishes. Later, the Monroe Doctrine was invoked to aid Mexico in a revolution that overthrew the French emperor Maximilian, to keep European states from invading to collect debts owed to European investors, and most famously during the Cuban Missile Crisis of 1962. However, American intervention in the region, usually to prop up regimes that were friendly to American business interests, has been very controversial, and has probably added to the instability that has plagued Latin American and Caribbean governments. It is also true that the United States never stopped foreign investors from investing in the region--this was why many countries wound up in debt to European powers in the first place. So it is probably too strong a statement to say that the Monroe Doctrine prevented European influence.