Both are about the romance between a poor girl and a man from the royal family and both involve a second female lead who does everything to get in the way.

A rebel fights the Japanese tyranny during its occupation of Korea.
Main lead must fight against Japanese officers and Korean aristocrats in both shows.

A patriotic woman disused as a male is part of a rebellious group out to remove Japanese corruption from her country out of Patriotism in both shows.
Both female leads are excellent at using a gun
Both female leads lost close family members are killed which is behind their motivation to be part of the rebel group.

Around the same time period. Features strong fighting women and focuses on patriotism. A lot of conflict between Japan and Korea.