The A.I. are sometimes an even bigger threat than real players. I was playing Operation supremacy once as Poland. I was streamlining through Germany and France (declared war first) then all of a sudden an A.I. decides to backstab me and captured and destroyed nearly all my core cities. I recalled some of my troops and got my revenge but by that time I lost France, Germany, and half my infrastructure. They didn't even embargo or anything just out of the blue declare war.
"Victorious warriors win first and then go to war, while defeated warriors go to war first and then seek to win." -Sun Tzu