What law passed to keep the United States from being drawn into war?

There have been various laws passed that have been meant
to keep the US from being drawn into war, but I think what you are most likely to be
talking about is the Neutrality Acts of the 1930s.

In World
War I, the Germans blockaded England using submarines.  US ships were put in danger of
being sunk as they tried to bring goods to England (just regular trade, not even
weapons).  The US Congress decided that one thing that got us into WWI was trading with
a country that was at war.  So the Neutrality Acts prohibited lots of kinds of trade
with countries that were at war.

If this is not the right
time period, let me know via message...