Factors leading America out of isolationism included all of the following except: a boxer rebellion b. spanish American war c. open door policy d. Monroe doctrine

The correct answer is the Monroe Doctrine.

The Monroe Doctrine focused on preventing future European influence in the Western hemisphere. President Monroe promised that the US would not interfer with any European colonies that were already established at the time of this doctrine (1823). However, Monroe went on to say that any future attempts at colonization would be met with a US military response.

The ultimate goal of this was to isolate the US from European conflicts.