This was the start of the Sino-Japanese War on July 7, 1937.
There is a claim that they were targeting it because it was the same as the Nogugyo incident.
Coming out of China
(Nogu Bridge Incident: When a Japanese soldier stationed in China went missing, the Japanese military claimed that he had been kidnapped by China, engaged in a small-scale skirmish, and used this as an excuse to start the Sino-Japanese War)
As for us, are we just trying to govern Gyeongsul-guk?