Destroyer of Worlds (Fleet of Worlds Series #3)

Worlds closer to the galatic core than Known Space are --or were--home to intelligent speciers. Some learned of the core explosion in time to flee.
Destroyer of Worlds opens in 2670, ten years after Juggler of Worlds closes; with refugee species fleeing in an armada of ramscoops in the direction of the Fleet of Worlds. The onrushing aliens are recognized as a threat; they have left in their trail a host of desolated worlds: some raided for supplies, some attacked to eliminate competition, ...