Barbarian+invasions

Huns push down Sassanids fought back, but pushed Germanic tribes inward Antonine plague started to hit soldiers in the borders, weakened defenses

Visigoths pushed down, separating west and east, under Alaric (sacked Rome in 410), Valens lost at Battle of Adrianople

Goths united under Theodoric Ostrogoths got Europe Visigoths got Iberia Vandals got Africa

Vandals take Carthage, one of Rome's main resource centers. This crippled Roman trade and severely hurt the economy.