The Knights Hospitaller, The Knights Templar, the Knights of Malta etc. Would these orders constitute terrorist organisations IYO? Most of them (all?) were not part of official national militaries but were instead militias composed of multiple nationalities and mustered to war on the say-so of the Pope, not any national government.
Sure, they could be classified as such. The Templars sure got the short end of the stick though when they were cast aside to the Spanish Inquisition.
I had KFC for dinner today, then watched Spearhead from Space with the girlfriend. She'd never seen a Pertwee serial before, but she decided she liked him after seeing The Five Doctors. Good times all around. I totally forgot how young the Brigadier used to be.