In The 24th Century... Life seems pretty good. But you know the old proverb, "What could go wrong?". The godlike Q put humanity on trial, introducing the Federation to the Borg. They analyze, see what they can assimilate, and when they can't. They destroy it, completely. The Federation was already building bigger, but now they're building badder. Ships that cut like a knife with a surgeon's precision. Turns out that helps a lot when the Dominion shows up. That's the long and short of it. Other stuff happened, too.

I wonder, did anyone ever think to have more than one grief counselor on a starship? Imagine the line.