Mahayana Buddhism is sometimes called Northern Buddhism. It is mainly followed by monks and nuns, and is largely found throughout China, Japan, Korea, Mongolia, Nepal, Russia, Tibet, and Vietnam.
The original tradition within Buddhism, Theravadan, continues to flourish even today, but around the First Century, a split began to develop. The Theravadans held fast to the ideas of monastic discipline, scholarly attainment, and strict adherence to the scriptures of the Buddha, while others saw this as being inflexible and difficult for anyone besides a monk to come to terms with. As a result, a movement to bring Buddhism to the "common people" began to gain popularity. This movement would eventually lead to the development of Mayahana Buddhism.
The Mahayana determined that Bodhisattva was a mandate not for individual perfection, but to save all sentient beings from suffering. Mahayana Buddhists take a vow NOT to enter Nirvana, even though they too strive to reach enlightenment. Instead their vow is to return to the world of suffering and assist all others in reaching Nirvana first, thus casting the role of Buddhists as compassionate protectors and saviors.
"The bodhisattva is translated literally as 'one whose essence is perfect wisdom' or 'one destined for enlightenment.' The essential characteristics of the bodhisattva in both sects are compassion, selflessness, wisdom, and servitude. The bodhisattva takes a vow: 'I must lead all beings to liberation, I will stay here until the end, even for the sake of one living mortal'. "