Hey, can you tell me what you base this claim on? It can't possibly be military intervention. Around 20 years before WWI we got involved in Cuba and fought a whole war over another nation's affairs. That's just off the top of my head. However, the US sent out military expeditions quite regularly to protect US interests abroad. We also deposed entire kingdoms (Hawaii) and fought off an entire rebellion in China (Boxer Rebellion). So I'm not sure what you're basing your claim off. The US has never engaged in the type of isolationism you're discussing.
Yeah, a general tendency to refrain from entangling alliances and interventions was the norm. That doesn't mean that we never strayed from that. We all know that we did. But nothing like the last century, is the point.
President Thomas Jefferson extended Washington's ideas about foreign policy in his March 4, 1801 inaugural address. Jefferson said that one of the "essential principles of our government" is that of "peace, commerce, and honest friendship with all nations, entangling alliances with none."[2]
In 1823, President James Monroe articulated what would come to be known as the Monroe Doctrine, which some have interpreted as non-interventionist in intent: "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."
After Tsar Alexander II put down the 1863 January Uprising in Poland, French Emperor Napoleon III asked the United States to "join in a protest to the Tsar."[3] Secretary of State William H. Seward declined, "defending 'our policy of non-intervention—straight, absolute, and peculiar as it may seem to other nations,'" and insisted that "[t]he American people must be content to recommend the cause of human progress by the wisdom with which they should exercise the powers of self-government, forbearing at all times, and in every way, from foreign alliances, intervention, and interference."[3]
The United States' policy of non-intervention was maintained throughout most of the 19th century. The first significant foreign intervention by the US was the Spanish–American War, which ultimately resulted in the Philippine-American War from 1899-1902.
http://en.m.wikipedia.org/wiki/United_States_non-interventionism