In those days, in Tang 'An Shi Rebellion' broke out against Emperor Xuan Zong, in the Korean Peninsula Silla rejected the meeting with the national envoy from Japan, and the other events happened, so that the foreign strain was growing higher and the defense of Kyushu had become urgent.
当時唐では、玄宗(唐)皇帝に対する「安史の乱」が勃発し、朝鮮半島では新羅が日本の国使との会見を拒否するなど、対外的な緊張が高まり九州の防備が急務となっていた。