Had a conversation a little while back that keeps echoing. The topic was a mildly racist event of some sort, I don't particularly remember what. The key question was this: "what's the big deal?" After all, the event didn't particularly change anyone's life. My answer at the time was along these lines: "the (nuclear) genie is out of the bottle, within 50 years any group on the planet can likely get hold of weapons that can render whole countries uninhabitable".
We've got lots of rouge states with old nukes. We've got barely stable states with ties to seriously unstable states being declared nuclear powers and apparently selling the core requirements out the back door. Within a few decades it seems to be a certainty that we'll have criminal organizations with minimal morals selling the various components you would need. One way or another, it seems pretty likely that by the time I'm dead it will be possible for any nut-job group with an axe to grind to get hold of something ridiculously destructive just by taking over some tiny country in the middle of nowhere with a barely-functional government that happens to have nukes.
There are other threats than nukes, other issues that require global cooperation, but the presence of nuclear weapons seems a decent minima. In 50 years we can expect that the genie will get out. Other genies may show up before then, but it seems unlikely that this particular one will stay capped for more than 50 years when it's already leaking around the edges.We need to get to the point where we can solve problems politically, rather than via armed conflict. To do that we'd need some sort of institutions that could provide international justice, policing and the like. But at a more basic level, we'd have to start teaching our children that racism, intolerance, and hatred are stupid, outmoded ways of thinking, so that by the time they are making the decisions and being asked to back those institutions they will be capable of being world citizens, of trusting that justice will prevail, of demanding that it does, and of being willing to accept their fellow citizens basic rights. Obviously there's a lot more that needs to happen, education, stable food supplies, etceteras, but that's more than one blog-post worth.