How did Mahayana begin?

Good place to start: Mahayana - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Mahayana)

What a rubbish answer.

Sorry, but as your question doesn't have a simple answer what where you expecting!
Did you read the link ?

No dramas. Was just expecting more than that.

Thanks for the help.

how did Mahayana begin?
As the Buddha's teachings spread from India, it encountered different cultures with different belief systems. As any other religion or philosophy, it changes over time. Once the Buddha's teachings reached China, it began to be assimilated and re-interpreted. The same happened when it spread to Tibet. It would be difficult to go in depth in such a medium as this.