I think it'd give everyone a little pep in their step to think we'd really make it another 150 years.
Nope. Civilisation sees many more or less imminent threats but does nothing.
There'd be a lot more movies and TV shows about aliens, especially regarding their conflicts with humanity, and military spending, maybe especially the space-based stuff, would go way up. It might also give rise to some sort of global military alliance, it might affect the politics between nations, might make them more unified. Hostility toward all aliens real and imagined would increase dramatically, so those aliens who are visiting us currently might be more dissuaded and rarer to witness. I feel it might also make sooner the point of First Contact (not necessarily with an alien species that's hostile toward us--I think the vast majority of them aren't), but I'm not sure why.
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