Because today it's easier to destroy a country completely without boots on the ground, so people won't have to occupy it and won't bother to rebuild it?

IMHO, major wars will only happen somewhere in Asia...between China, Russia, India and Pakistan (all nuclear powers). They all have border issues are relatively large countries and China and India have potential to be local superpowers. China will need Lebensraum and move into Siberia and that might start it all. USA will probably seek to sell arms to both sides and stay out of it:).