American Airlines currently sells seats from Seoul to Atlanta (via Dallas) for just $300 round trip. That's an amazing fare – even if you just use it as a one way from Asia and throw away the return (I would not recommend that though!)
Note that it does not work in reverse from the US to Asia.
The best way to make use of that fare is book two trips and nest the itineraries, or use AAdvantage off-peak 20,000 miles to Northern Asia in order to get to Seoul and back.
The fare will earn 100% miles with AAdvantage – that's 15,144 miles. If you are an Executive Platinum with American, you can upgrade your seats to business class.