There were roughly four generations of students, comprising the pre-war students (training 1921–1935), students who trained during the Second World War (c.1936–1945), the post-war students in Iwama (c.1946–1955) and the students who trained with Ueshiba during his final years (c.1956–c.1969). As a result of Ueshiba's martial development throughout his life, students from each of these generations tend to have markedly different approaches to aikido. These variations are compounded by the fact that few students trained with Ueshiba for a protracted period; only Yoichiro Inoue, Kenji Tomiki, Gozo Shioda, Morihiro Saito, Tsutomu Yukawa and Mitsugi Saotome studied directly under Ueshiba for more than five or six years. After the war, Ueshiba and the Hombu Dojo dispatched some of their students to various other countries, resulting in aikido spreading around the world.