The technologies of war developed since the end of the Cold War (and indeed, in the last decade of the Cold War) remain untested in high intensity combat against sophisticated, resourceful opponents. The NATO alliance (and its most powerful members, in non-alliance conflicts) have soundly beaten foes with aging air defense systems, non-existent air forces, and trivial offensive capabilities.
It remains to be seen, however, how effectively NATO would fight against a determined, well-trained opponent with relatively modern technology. Recent events in Ukraine have, for the first time since the Cold War, raised the spectre of direct conflict with Russia. If diplomacy fails and politics push the alliance into war, these are the weapons NATO will need to worry about the most.