A nuclear war will never happen because humans are becoming more stupid. We know that if you just anyone have children genetic mutations happen really fast and get really bad. For example, bad mutations in the eye outnumber good ones 2/1 so when we have shit like glasses to help people not die from their terrible eyesight and can pass down their eyesight to their children who then have a chance to make their eyesight worse through genetic mutation, in a couple generations all humans will need to have artificial eyes. Now consider that our brains make up 80% of our genome so 80% of all bad mutations will happen to our brains.
A nuclear war cannot happen because we will be too dumb to build or maintain nukes. Although that doesn't necessarily mean that a nuclear war can't happen in the next 100 years. My actual and real belief is that we will never make it to Mars, what is more likely is that we return to a pre-industrial age not through nuclear but through the natural genetic decline of humans.
Don't take this as me advocating for eugenics. When you implement eugenics you choose "good" traits but you also indirectly choose really really bad ones