Nuclear weapons and global economics ensure there will not be anymore wars like WW1 and WW2.

Look at the two big rivals today - China and the USA - their currency is pegged.. war is not beneficial to either of them.

The only possible war I can think of that could be considered a world war is if Russia becomes like Germany before WW2 and rearms and revamps their economy and feels like pushing others around. Even then, with the way world economies are set up, war wouldnt benefit them.