"Natural Catastrophe"

Cost Mass Tech Level Duranium Tritanium Molybdenum	Large Weapons Max Large Size Small Weapons Point Defense Super Weapon
Max Fuel Max Ord Max Repair Max Cargo	Engines Generators Power Bank
Armor Limit Shield Limit	Pod Bays
Crew Size Passengers	Fighter Bays Fighter Bay Size Construction Bay Size
Max Speed Max Hyp Jump Evasive Bonus Attack Bonus Warp Drag Factor Warp Signature Scan Range Tractor Beam Cloak Fuel Burn
Vulnerability To Weapons Fire Parts / Hull Control Systems Engines Hyperdrive Lifesupport Critical (Soft Spot)

An ion storm / herd of planet eating goats / Chup plague which moves round the map, causing so much disruption it impels locals to migrate or die.

Example: one theory about why the Roman Empire fell is that the Mongol Hordes pushed the Huns out of their old lands. The Huns in turn headed into the Empire.

As a scenario driver, a wave of something Bad moving into the galaxy will force huge migrations and wars as people scramble to escape its path.