It's a serious fact - any reversal or serious downgrade of economy or near bankruptcy in any of the top powers fortunes will prompt trigger happy generals to start a war and the way countries are interlinked today, probably a regional war will go multinational quite soon.
Well, there is a positive story also possible: China's Peaceful Demise.
Just like Soviet Union dissolved peacefully. So, as of now, we don't know ...they could dissolve peacefully, or go the out the "hitler way", which means conflicts.