Question

What caused Nineteenth-Century Isolationism?

Answer 1

President James Monroe's "Monroe Doctrine."

In 1823, he stated this doctrine, saying, "In the wars of the European powers, in matters relating to themselves, we have never taken part, nor does it comport with our policy, so to do. It is only when our rights are invaded, or seriously menaced that we resent injuries, or make preparations for our defense."