Eventually Mahayana became the largest major branch of Buddhism, due to its integration with the early schools. According to Wikipedia, “The Mahayana tradition is the largest major tradition of Buddhism existing today, with 53.2% of practitioners, compared to 35.8% for Theravada and 5.7% for Vajrayana in 2010.” (htt)
The early beginnings of Theravada spread back furthermost in history. It is descending from an elder group called the Sthavira that broke away during the Second Buddhist Council, in the 3rd century B.C. Later the split became more official about a hundred years later with the Indian Emperor, Ashoka’s, decision. He decided to expel monks who failed to agree to the terms of the Third Council. There are two different goals in between