The field was 'evened' so effectively, in fact, that the nobles began to hire the best of these clans' so-called 'ninjas' as spies and mercenaries. Unable to stand up in traditional combat to the expensively funded and heavily-outfitted samurai, some of these resistant clans developed unique martial-arts techniques and fighting strategies based on mastery of one's environment, along with weapons based on common tools and simple farming equipment, in order to even the playing field in combat. During the feudal era in Japan (largely beginning in the 15th Century), many isolated rural clans were resistant and even hostile to the idea of being ruled over by the laws of nobles - especially when they were being enforced by often oppressive samurai. Let's be clear about one thing upfront: Ninja were (and, depending on who you ask, still are) a real thing.