Answer:
The Whiskey Rebellion. In 1794, farmers from Western Pennsylvania rose up in protest of what they saw as unfair taxation and provided the new nation, and George Washington, with a looming crisis. In 1791, Congress approved a new, federal tax on spirits and the stills that produced them.
Explanation (more notes):
The violent climax occurred in the area around Pittsburgh in the summer of 1794. Following a pattern established in the American Revolution, local farmers had begun holding special meetings to discuss their opposition to the tax as early as 1792. A mass meeting in Pittsburgh declared that the people would prevent the tax from being collected and one tax collector was even tarred and feathered in protest.
President Washington soon declared such meetings unlawful, but among ordinary settlers in western Pennsylvania he was often seen as just another large-scale landowner from the east who didn't understand local conditions. Many men would not back down in the face of what they considered an oppressive and unjust tax. Matters came to a head when an angry crowd who refused to pay the tax harassed a federal marshal, tax collector, and a handful of federal soldiers. The troops surrendered and the marshal's house was torched. Other minor protests soon swept western Pennsylvania and there were rumors of holding a convention to discuss secession from the United States.
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