Tesla and SpaceX CEO Elon Musk has a lot of ambitious dreams but he also seems to worry quite a bit about apocalyptic dangers — for example, he has talked at length about the potential threat that artificial intelligence poses to humanity’s existence. But it’s not only AI that keeps him up at night, as he seems concerned that humanity might ruin itself through war before any killer robots even have the chance.

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In an interview with GQ, Musk says that humanity’s ability to colonize Mars would be severely jeopardized by getting into another world war that would cripple our ability to invest and cooperate in the project of sending people to Mars.

“I don’t think we can discount the possibility of a third World War,” he says. “You know, in 1912 they were proclaiming a new age of peace and prosperity, saying that it was a golden age, war was over. And then you had World War I followed by World War II followed by the Cold War. So I think we need to acknowledge that there’s certainly a possibility of a third World War, and if that does occur it could be far worse than anything that’s happened before. Let’s say nuclear weapons are used. I mean, there could be a very powerful social movement that’s anti-technology. There’s also growth in religious extremism. Like, I mean, does ISIS grow?”

Well, those are some cheery thoughts!

Musk is right to be worried about the possibility of another global war, particularly if ISIS gets its wish and sparks a “clash of civilizations.” If that were the case, it would be really hard to imagine humanity devoting the resources necessary to colonize Mars, among other things. So let’s just cross our fingers and hope that doesn’t come to pass.

Check out Musk’s full interview with GQ at this link.