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Enterprise Season 3 opens with a Xindi ship coming out of warp over Earth and cutting a 20 mile wide trench across Florida. Earth didn't know the Xindi existed at the time, had no idea it was coming or why.

Spoiler alert: the Xindi had been given faulty/false information that Earth was planning to attack them, by some other mutual enemy. IIRC it had to do with that "temporal cold war" thing they tried to push, which I'm convinced was someone in a writing room saying words without thinking about what they meant. What ensues is basically the Hell episode of Voyager stretched across a season.