Eihei Dogen is a highly significant figure in the history of Buddhism, particularly in Japan. He is the founder of the Soto Zen school, one of the major branches of Zen Buddhism in Japan. Dogen's teachings and writings have had a profound impact on the development and spread of Zen Buddhism, not only in Japan but also in other parts of the world.

One of the most significant contributions of Dogen to Buddhism is his emphasis on the practice of zazen, or seated meditation. He believed that zazen is the key to experiencing the true nature of reality and attaining enlightenment. Dogen's approach to meditation was unique in that he emphasized the importance of posture, breathing, and concentration in the practice of zazen. He also stressed the idea of "just sitting," which means that one should not strive for any particular goal or outcome in meditation, but simply be present in the moment.

Dogen's teachings also had a significant impact on the understanding of impermanence in Buddhism. He emphasized the concept of impermanence as a fundamental truth of existence and encouraged his followers to embrace it rather than resist it. This understanding of impermanence is a central aspect of Zen practice, and it is believed to lead to a deeper understanding of the nature of reality and the true self.

Another significant aspect of Dogen's teachings is his emphasis on the unity of practice and enlightenment. He believed that the practice of zazen is not separate from enlightenment but is, in fact, the actualization of enlightenment. This idea challenged the traditional view that enlightenment is something that can only be achieved through rigorous ascetic practices or sudden flashes of insight. Dogen's teachings opened up the possibility of enlightenment for everyone, regardless of their background or level of spiritual development.

Dogen's impact on the history of Buddhism is not limited to his teachings and writings. He also played a crucial role in the institutionalization of Zen Buddhism in Japan. He established the first independent training monastery for monks and nuns, which became the model for other Zen monasteries in Japan. He also trained many disciples who went on to become influential Zen masters, spreading Dogen's teachings and lineage throughout Japan and beyond.

In conclusion, Eihei Dogen's significance in the history of Buddhism cannot be overstated. His emphasis on zazen, understanding of impermanence, and the unity of practice and enlightenment have had a lasting impact on the development of Zen Buddhism. His teachings continue to inspire and guide practitioners of Zen, and his legacy lives on through the Soto Zen school and its many branches.