I heard a theory a while back (NPR or BBC? It was a reputable source) that suggested that growing nationalism in China may soon put the country in a position to start world war three. That got me wondering what society looks like leading up to major wars. Are there normally telltale signs that war is coming? Or is every war so different that it's hard to predict? Would we know if we were headed for WWIII right now?
There's no one answer that fits every scenario, economic strife, a leader under pressure, or a leader with ambitions outside their borders often leads to trouble.
But socially, I suppose you could look at migration - if it suddenly increases in a country is it a certain group or a mixed group thats migrating?