Homefront deals in the fictional future where Kim Jong Il passes away and his son unites North and South Korea. They then invade Japan and become a massive superpower.
Long story short, the unified Korea attacks America and succeeds.
Homefront is not a game about defending America from an invasion. America has already been invaded. It is now time to fight back!
From the several videos and articles so far Homefront is shaping up to be a solid shooter with an immersive single player.