" However, this posture did not necessarily mean that America's policy of refraining, except when absolutely needed (as in the Spanish-American War, the War of 1812, and the First World War), from military engagement in the military conflicts of other countries or regions literally "caused" those countries to use military force against one another with impunity.
In discussing the historical underpinnings of American isolationist policies, Paul S. Boyer (397) noted that for much of its first one hundred-plus years, America focused its overseas military activities on places and events in the Western Hemisphere. This policy was a byproduct of the belief, prevalent through to the time of the First World War and then again until the Second World War, that America's interests were best served by ensuring that her borders were secure, that her neighbors were not a threat to national security, and her trade relations with potential combatants protected. Even when the U.S. entered World War I, it did so as an "associated power" so as to avoid any obligations that might emerge from a binding military alliance. Of course, Boyer (397) says, the involvement of the U.S. in that "Great War" was a definitive element in the ultimate defeat of the Germans.
In analyzing the origins of the Second World War, historian A.J.P. Taylor (35) makes reference to American isolationistic policies but also notes that after World War I, America very much wanted a peaceful Europe