Watch this video to take a walk down the time lane. Note that the spread of Buddhism from South Asia to Japan was not linear, rather, it was radiative along the journey.
Click the video below to get a grip on the initial period when Buddhism was introduced to Japan. This includes a briefing to Prince Shotoku's embrace of continental ideals and patronage of Buddhism. The video also covered the endorsement of Buddhism by Emperor Shomu and his construction of Todaiji.
Browse this timeline of Buddhist dissemination and development in different parts of the world. (Buswell & Lopez 2013, xxi). This section touches on the introduction of Buddhism to Japan and the dissemination of Buddhism in Asia in large. It merits attention that Buddhism had journeyed from the Asian continent to Japan via the Korean peninsula. You may also compare Japan's handling of Buddhist with its Asian counterparts. Could this suggest the peculiarities of the political contexts in each regimes as well?
Page reference:
Buswell Jr, R. E., & Lopez Jr, D. S. (2013). The Princeton Dictionary of Buddhism. Princeton University Press.