A few scenarios could set it off really..

Miscalculation in Syria right now could do it. Turkey might actually end up at war with Syria soon. That is extremely possible.

Another one is Israel & Iran. One incident in the Persian Gulf could set that off. US & UK could get involved.

China & Japan are infamously stubborn, both countries put war before losing pride. Panetta confirmed this recently.

India and Pakistan is always a powderkeg waiting to blow. When Islamists seize power in Islamabad, India will play hardball.

As for Korea, give it till June 25 in 2013. 70th anniversary of the end of the Korean War.