Warmatrix

The Goths, who originated in northern Europe, slowly migrated southeast into eastern Europe, eventually reaching as far as the Black Sea. They were divided into Visigoths ('Western Goths') and Ostrogoths ('Eastern Goths'). They had battled with the Roman empire several times since 247 CE, though had always been repulsed, the last time in 364 CE. In the late 4th century CE they were hit from the east by the Huns, who drove them westward. In 376 CE many of them reached the river Danube and asked the Roman emperor Valens for permission to cross the river and migrate into the Roman empire. Valens agreed, afraid of strife if he refused but also hoping to use the new manpower to bolster his army. The migration was very harsh: the old and sick were left behind to the Huns and only the young and strong were allowed in. Nevertheless the Romans proved unable to feed the still large group that was accepted. Roman governors proved corrupt, food was reserved for the garrisons, the Goths were denied access to markets and were forced to sell some of their people into slavery. When the Romans even tried to assassinate some Goth leaders, they broke out and started a revolt.
Initially the Goths tried to capture Adrianople, but lacking siege equipment, they could not take the city's walls. Instead they kept themselves fed by plundering the countryside, the bulk of the Roman army being too busy elsewhere to stop them. In 377 CE both sides fought the Battle of the Willows, which was inconclusive. Raiding was insufficient to feed the Goths, so they moved south and managed to break out of the Roman containment. Emperor Valens personally led an army to stop them, but was defeated at the Battle of Adrianople. The victorious Goths again tried to storm the Roman cities and again failed, so they spent the next two years plundering Thrace, Thessaly and Dacia.
In 380 CE they split into two armies, probably because it was hard to keep a large force properly supplied. The Greuthungi moved north into Pannonia. They met an army led by the western emperor Gratian and were defeated. The Tervingi, led by Fritigern, hero of the Battle of Adrianople, moved into Macedonia, extorting towns rather than sacking them. In 381 CE forces of the western Empire drove them back to Thrace. A year later peace was made. The Goths became part of the Roman empire as agreed six years earlier, though now they were treated much better. They were settled in Pannonia and Moesia and became foederati, barbarian soldiers in employ of the Roman empire. Nonetheless the relationship between the two parties remained an uneasy one and (much) later the barbarians carved out kingdoms in Italy and Iberia.
The plundering of the Balkans by the Goths that lasted several years and damaged the economy of the Roman empire, which was already weak. This eroded the tax base of the state and in turn its army deteriorated too. Other tribes copied the example set by the Goths and slowly started to infiltrate the Roman empire. Looking back, the Gothic War can be seen as the beginning of the end of the western Roman empire.