History, Originality & the Present
1. Morihei Ueshiba changed what he called his art a few times, however, he finally settled on the name Aikido.
2. By the late 1940's and early 1950's Tomiki and Shioda broke away from Ueshiba to establish their own organizations.
3. Throughout the 1950's up to 1970, the primary style was that practiced and taught by Morihei Ueshiba, Kissomaru Ueshiba and Koichi Tohei as the primary conveyors. This is not to give slight to others not mentioned, but these were the three main lights.
4. In the early 1970's Koichi Tohei startd Ki No Kenkyukai Shin Shin Toitsu Do Aikido.
5. During the 1960's and 1970's the main "Hombu" school (Aikikai) has sent instructors to various parts of the world. Oftentimes these would then start up an organization in their area and give it a name with themselves as the head. Each would pledge allegiance to the Aikikai and each could be as different from all of the others under the same rubric of Aikikai as say and Yoshinkai and Ki Society dojo might be from each other.
6. Primarily during the 1980's and 1990's many "national" organizations have been born because the natives of the particular country had disagreements with either Japan or the head of the branch organization. Some very highly regarded aikidoka have chosen to not be affiliated with any organization.
7. O' Sensei's religion and beliefs were in the Omoto Kyo sect of Shinto, a fairly esoteric sect even for Shinto. However, he made it clear that Aikido, while embodying his understanding of some of the theology of this sect, was not Omoto Kyo and that it was not necessary for Aikidoka to belong. Quite the contrary he made enough statements throughout his life that he saw Aikido as helping all religious systems to fulfill their highest goals of establishing peace.
Finally, all of these various pieces of history, mythology and traditions which surround Aikido have been debated for quite some time. One of the problems stems from O' Sensei in that he might relate the same event differently on different occasions. Another problem is that his students like many students around the world, oftentimes heard what they wanted to hear and ignored what they did not understand or thought was "old fashioned". The consequence of these natural occurences has been different emphases by different Aikidoka.
All provides a beginning answer to the basic question of why there are so many different styles of Aikido.