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It's not Ender's Game, and I'm not sure if it's Time Traders, as I don't recall anything about time travel. I am pretty sure it was just a normal Alien Invasion story, as I was talking about how the Lizards in World War had advanced anti-missile systems that were completely ineffective against primitive artillery, and they commented about how it was similar to the psychic aliens being unable to fight against human technology.

A stranger at a party a few years back told me about a book, and all I can remember was that it involves an Alien Invasion. The aliens have no weapons, though, as they are powerful psychics, and every sentient race in the galaxy has crumbled before their might... except for some reason humans aren't developed enough to utilize this sort of psychic form of communication, and are therefore immune to attacks that utilize it.