The Korean regular force, which had never experienced a full-scale war except troubles with 'wako' (Japanese pirates) or the Joshin tribe, was overwhelmed and completely defeated by the Japanese military force, which was equipped with a large amount of guns after the Sengoku period (period of warring states).
倭寇や女真族との紛争以外本格的な戦争経験がない朝鮮正規軍を、戦国時代(日本)を経て大量の鉄砲を装備した日本軍が圧倒し連戦連勝を重ねた。