It is correct that Germany's resuming maritime warfare was the main cause that caused the war. The U.S. wanted to stay out of it, supposedly, but they were already making preparations for a war beforehand. Whether it was just precautionary or planned is a little harder to say. But the Germans sank many U boats and other ships and the U.S. did not jump in until 124 Americans died in the bombing of the Lusitania. However, isolationism did not take place until after WW1 and was actually caused by that first war, which would be one way that it changed foreign policy.
When Germany first started getting out of control under Hitler later on, the U.S. would not get involved. For every major event, the U.S. came up with another Neutrality Act until it became clear that we had to intervene.
