The Whiskey Rebellion happened in 1794—when settlers in the Monongahela Valley of western Pennsylvania protested against the new federal tax on whiskey, which the settlers shipped across the mountains to earn money. It was the first serious test of the federal government. Washington ordered federal marshals to serve court orders requiring the tax protesters to appear in federal district court. By August 1794, the protests became dangerously close to outright rebellion, and on August 7, several thousand armed settlers gathered near Pittsburgh, Pennsylvania. Washington then invoked the Militia Law of 1792 to summon the militias of several states. A force of 13,000 men was organized, and Washington led it to Western Pennsylvania. The revolt immediately collapsed without violence.