The reason Kukai came back to Japan so soon was considered as follows; the Great Tang Empire was in a terminal state, and as the outbreak of the Anshi War suggested the unstable political circumstances, oversea students were not well-treated.
空海が帰国した理由は、当時の大唐帝国はすでに末期状態にあり、安史の乱が起こるなど国情が不安定で、留学生たちの待遇も不十分であったことが考えられる。