We are never going to see another World War. The world has changed. Tech and the way information is transferred and readily available has changed people's views. While there is communism and dictatorships like N. Korea and China, we have a relationship with the big players like China. This was evident in the Iraq war. Iran, China, ect.. could have joined in and it could have gotten really bad really quick but that didn't happen.

The real threat is with small fractured groups. Groups like ISIS, terrorists and rebels in countries like Syria, Libya, Egypt, ect...

Its hard to deal with small groups and cells of terrorists with no permanent location, but groups like these have been around for hundreds of years and will always be there. You just try to keep them suppressed and under control.