In the medieval period, the principle of the "divine right of Kings" was adopted by most philosophers. In other words, warring against your own government was always immoral.
When Charles I was king of England, the notion arose as to the acceptability of a legitimate rebellion. Oliver Cromwell was a member of Parliament who set forth the argument that when a King becomes corrupt, it is not only allowable, but right to overthrow that king.
The use of gunpowder transitioned the world out of the medieval period.
Cromwell's philosophy would be adopted by later revolutionaries such as Thomas Jefferson and the Americans.
DECISION: When, if ever, is it proper to attempt to overthrow your government?