The 20th century was by far the most violent century in all of recorded history. The vast majority of that violence was in the first half, namely World Wars I and II. The 19th century had been the most violent century before that. The 18th century had held the record before that. The same reasons that wars tend to become more violent as they progress apply to the larger view over the centuries. Toss in the fact that technology allows for larger armies. I would expect this trend to continue.
It makes sense that after the larger wars, things become quiet for some years. Exhaustion from war requires time to recover. Maybe human violence is like earthquakes. Maybe we need the smaller wars to relieve the stress? Otherwise, WATCHOUT! It has been more than 60 years since the last major war. Not that