We went from 4-5 countries getting nuclear weapons in the first 15 years, and an era of about 60 nuclear tests each year in the 30 years after that, to the current era where it's about one country every 10-20 years gaining nuclear weapons and basically no tests happening. I'd say that's a massive improvement.

We've also mostly stopped with firebombing, and have seriously dialed back the chemical and biological weapons that were much more popular in the WWI/WWII era.