Actually that would be to tell if it is an actual occurrence. We know sci fi tropes because we make them up.We won't be able to tell if it is more than a Sci-fi trope until we meet some aliens of our own.
As much as we ponder it we never actually seriously look into how society would or should adapt to the existence of aliens, and we shouldn't, because we don't know if aliens exist at all. There is a whole other side to space-civilization sci fi that involves humans being the only intelligent life in the galaxy (or universe), and in that regard it would be countries competing against each other for control over planets and stars, and then colonized planets slowly becoming independent human administrations that develop their own countries and problems.
But alien and alien economic and diplomatic interaction would be a nightmare to administer if planets were not unified. Individual regions of planets would be dictating their own policies for trade, which would easily screw over the rest of the planet's trade interests. Also, imagine attacking a planet without upsetting everyone on it, or worse, one country sides with an alien invader to allow them to invade a neighboring country, and then THAT alien invader having its own geopolitical rivalries and wars at home.
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