Mahayana Buddhism originated during the reign of Kanishka,it was presented in a new form of Buddhist school of thought,that was the time the Buddhist scholars began to write their thoughts in sanskrit,the worship of images of Buddha and the rituals started.It spread quickly to the neighbour countries,Chine,Tibet as well as the far off countries like Japan & Korea.
Kanishka convened a Buddhist council in Kashmir in 72 AD,where the scholars met and discussed the new idea of Buddhism,it was during this period it underwent a change.It totally changed the Hinayana concept of reverence of Buddha,like worshipping the symbol of elephant,lotus,pada paduka and depicting his enlightenment with the peepal tree and in Mahayana these were replaced with images of Buddha along with the Bodhisattvas.
According to Mahayana Buddhism that Buddha had passed on many secret teaching of compassion to his immediate followers and those who follow their life according to his teachings as Bodhisattvas.Mahayana Buddhism emphasizes its followers to emulate the lives of Bodhisattvas as being kind and generous to all the living beings and that's being the way to one's enlightenment.
Zen Buddhism & Tibetan Buddhism comes under the Mahayana Buddhism.
Credit: Thomas Alexander