> Then why is violence worldwide decreasing?

Actual violence mostly occurs when one side is willing to use violence and the other side has enough belief in their ability to resist (including in that belief that the first side will back down before resorting to force) to compel the first side to actually resort to violence to achieve their actual aims, to which violence is usually merely a means. States becoming more willing to use violence and gain greater capacity to accurately (at least, avoiding false negatives) target that violence might plausibly result in populations becoming more compliant without actual resort to violence (or, at least, more quick to capitulate on an issue once the state first responds violently on it), reducing total active violence but increasing repression through the omnipresent threat of violence.

(Also, violence done “in [society's] name”—mostly state violence—and violence in total aren't the same thing; it's also plausible that total violence might decrease while, perhaps even because, state violence increased in a way which eliminated more non-state violence.)

And, are you counting something like what China is doing to the Uighurs in what you count as violence?