Yes your subjects are common. However, I studied class development in Antebellum America and teach colonial history, Civil War and Twentieth Century history. Last semester I was asked to take over an Environmental History class because the person teaching it was no longer able to. Another example I can give was when I took a History of Human Rights class and my professor had focused on Indian and Pakistani history in his studies. What you focus on in your studies is not necessarily what you will be teaching. But what you study will prepare you to teach other relate-able historical subjects. I have found it very rewarding and have enjoyed branching out but that is more because I enjoy the education process. Remember teaching is not all about passing on knowledge, teaching is also about empowering.

Another suggestion do not just rely on your history classes. When I first started out I was focused on, believe it or not Central Asian history. I took a class on Hinduism and I found a political science class on politics in Asia. The other academic departments might offer classes that will relate to your historical topic. I would also suggest looking into Korea language classes if you intend on pursuing this. And don't worry if you change your mind later on. Like I said earlier I started out focusing on one topic and completely switched it up later on.