Assertion: Buddhism spread to South East Asian countries and also to east Asian countries after its origin in India.
Reason: Indian Buddhist teachers travelled to faraway places, carrying texts to disseminate the teachings of the Buddha.

Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

With the spread of Buddhism to East Asia, pilgrims like Fa Xian and Xuan Zang journeyed from China to India, seeking texts that they brought back to their homeland and translated with the help of scholars. Indian Buddhist teachers also embarked on travels to distant places, carrying texts to disseminate the Buddha's teachings.

Buddhist texts were preserved in manuscript form for several centuries in monasteries across different parts of Asia. In modern times, scholars have prepared translations from Pali, Sanskrit, Chinese, and Tibetan texts, ensuring that the profound wisdom of Buddhism continues to enrich and inspire people around the world.