Shay's Rebellion took place in Western Massachusetts in the period 1786-1787. It was caused by the small farmers in the area reacting angrily to crushing debt and heavy taxation. The huge war debt of the American government trickled down to the farmers by way of a head tax, which meant that small farmers with large families had to pay more than rich merchants with smaller families. Failure to pay could lead to loss of lands and imprisonment.
Shay, a veteran of the Continental Army and Day organized semi-armed mobs and threatened the legislature and the courts, and they attacked the Springfield armory, although they were driven off, and the failure of that attack (and the arrival of Massachusetts militia reinforcements) led to the collapse of the Rebellion.
The results of the rebellion were calls for more effective central government and helped lead to the ditching of the Articles of Confederation in favor of the stronger Constitution.