In the 19th century, when it comes to Korea, Japan was doing the heavy lifting. Queen Min (who couldn't be pinned down by Korea's intensely patriarchal society) developed a spy network in Imperial Nippon to track the modernization of its military as Japanese ambassadors practiced the same gunship diplomacy they learned from Europe.

She became such a problem, Japan sent a literal platoon of ninjas to kill her. Which they did, brutally.

The Joseon dynasty fell to disarray and collapsed in short time, though the assassination of Queen Min wasn't causal so much as Japan was ready to put its war fleet to use, and Korea, with its sweet harbors and strategic significance was a choice target for a test run.