Simplify the following text for a Grade 11 native English-speaking person.
Original: A militia that had been raised as a private army defeated an attack on the federal Springfield Armory by the main Shaysite force on February 3 , 1787 , and four rebels were killed in the action .
Simplified: A militia that had been raised as a private army defeated an attack on the federal Springfield Armory by the main Shaysite force on February 3 , 1787 .