Thank you for asking me.
A little historical background of Buddhism will answer your question. During the Buddha's time, his teachings were all memorized by the learned monks and passed down as such. After a few hundred years, differences in interpretations began to appear. A lot of Brahmins from the Brahmin religion (modern day Hinduism) became Buddhists. During that time the emperor was a Buddhist. His name was King Asoka. Naturally, all would like to become Buddhists! Because of these differences, King Asoka called for a council of senior monks to confirm the authenticity of the Buddha's teachings. The council of learned monks recited and confirmed the full text of the teachings which had been handed down by verbal recitation. They referred to this confirmation as the text of the elders (senior monks). In the Pali language it is called Theravada, which is the tradition that I follow. The Brahmin group decided to have their own version and called themselves the Great Vehicle (Great Wheel), in Pali, Mahayana. They then belittled the Theravada by calling them Lesser Vehicle which in Pali is Hinayana.
The Mahayana spread towards the north-west to Afghanistan, the Silk Route to China, Korea, and Japan. While the Theravada spread to the south to Ceylon (Sri Lanka), and then up north-east to Burma, Thailand, Laos, Cambodia and Vietnam.
Being very practical teachings based on universal truths, Buddhism was able to be accepted by the different communities. They could practise Buddhism without having to change their cultures and customs. That is why we have Tibetan Buddhism, Chinese Buddhism, Japanese Buddhism, and who knows Western Buddhism!
The beauty of Buddhism is that although there are such varieties, the basic teachings of the Buddha are the same. The difference is actually in the rites and rituals, and some other minor subjects.