What is Neutrality Act Of 1794?

Legal Definition
The Neutrality Act of 1794 makes it illegal for an American to wage war against any country at peace with the United States. The Act declares in part:

If any person shall within the territory or jurisdiction of the United States begin or set on foot or provide or prepare the means for any military expedition or enterprise...against the territory or dominions of any foreign prince or state of whom the United States was at peace that person would be guilty of a misdemeanour

The act also forbids foreign war vessels to outfit in American waters and sets a three-mile territorial limit at sea.

The act was amended several times and remains in force.
-- Wikipedia