To what areas had Buddhism spread to by 600 c. e.?

It spread to Nepal, Tibet and China where it slowly grew alongside with other Chinese religions.

The spreading of Buddhism it spread to Nepal, Tibet, and China where it grew slowly alongside Chinese religions, by the ninth century, Buddhism was well established in China and spreading to neighboring countries, too!. It reached Korea in the fourth century, and then it spread to Thailand, Combodia, Malasya, and Caos, and by the sixth century it was established in Japan. By 600 CE in India, Buddhism spread to Japan, Siam, Burma, Annam, and Kapilavastu.