sometimes used interchangeably with the modern term is the strategy and tactics of unconventional warfare, guerrilla warfare and espionage purportedly practiced by the ninja. Ninjutsu was a separate discipline in some traditional Japanese schools, which integrated study of more conventional martial arts (taijutsu) along with shurikenjutsu, kenjutsu, sōjutsu, bōjutsu and others. While there is an international martial arts organization representing several modern styles of ninjutsu, the historical lineage of these styles is disputed. Some schools claim to be the only legitimate heir of the art, but ninjutsu is not centralized like modernized martial arts such as judo or karate. Iga Ryu claims to be the oldest recorded form of ninjutsu, and claims to have survived past the 16th century.