Out Of The Dark by David Weber

Humanity greets an apparently benevolent extraterrestrial arrival whose advanced technologies and promises of cooperation win rapid acceptance — until the aliens' true, predatory nature and covert biological tactics are revealed and societies begin to crumble. As governments falter and the invasion unfolds, a disparate mix of soldiers, scientists and ordinary people must improvise defenses, adapt technology and mount a desperate resistance, forcing wrenching moral and political choices while fighting to reclaim their world.

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