Here's the official trailer for Homefront
which explains how the Koreans came to take over the US:
While I'm really looking forward to Homefront
(it was one of my top games last year) I'm having serious problems with the notion that Korea is really a major threat to the US, much less most of the Asian world. Suspension of disbelief is one of the most important parts of a game and this is really a major hurdle for me right now as North Korea is having enough problems feeding their population
missiles to really be a credible threat to the US (disclaimer, I'm a military brat so patriotism++ here).
That said I'm very anxious to see more of the game this year and hopefully I can get past the premise a bit.