Japan attacked Joseon at 1592. Japan had muskets, but Joseon only had bows. So the Japanese amry reached Hanyang in a few weeks. At that time, numerous of blameless people was killed. The war was lasted 7 years. 

Battle of Hangju(apron over the skrit) is another famous battle during Japaness Invatuion of 1592. Women helped the men by carrying rocks in their aprons. 

But, Imjin war's most best hero is Lee Sun-Shin in the ocean. He won many naval victories against Japapnese army. He made turtle ship, that is made ships safe from fire attacks, and it could destory Japan ships easily. He won Hansando strategy. But he died in Noyrang strategy. He left a famous word 'Don't tell I'm dead.' 

Thank you for reading!