There have been many variations to explain the reason for the Gothic exodus from the Baltic Area in ancient times. No doubt there was no pressure from non-Germanic groups.
An outright famine due to deteriorating climatic conditions could be one explanation. There were likely a limited migration of a few aristocratic clans.
They might then in turn have organized the local population in given their name to it. But thedisappearance of incineration burials makes it more probable that all population strata were effected in Goetaland. The local provenance of the Wielbark culture in Poland may have been caused by rapid assimilation of the Goths.
Why did the Goths migrate first to the southern coast of the Baltic? One possible reason is that the migrators followed the traditional Amber Way, the old trade route linking southern Scandinavia with the eastern Mediterranean as early as 1800 BC.
Sweden historically “looked” east and south, not west (which was the way Norwegians “looked”, for instance). The other side of the Baltic was the traditional area of interest. If one wants to go southeast from Goetaland you end up in the Vistula delta and the surrounding area. The ethnogenesis occurred between the rivers Oder and Vistula.
The Barbarians were equally effective on the sea. They had probably learned their maritime skills on the Baltic for it would be impossible for a land-borne people to adapt to maritime warfare so fast.
In Italy the Ostrogoths created a Kingdom:
493 – 526 Theoderic the Great invaded Italy 489; he was recognized as king 493.
526 – 534 Athalaric (maternal grandson)
534 – 536 Theodahad (son of Theoderic’s sister)
536 – 540 Witigis married a sister of Athalaric; deposed, died 542.
540 – 541 Ildibad
541 – 552 Totila (Baduila) (nephew of Ildibad)
Byzantine conquest of the Ostrogothic kingdom in Italy 552.
The northern barbarians contributed to the fall of the Roman empire during the Era of Great Migration. Now there is another such migration, maybe. Now the emigration is from a former part of the Roman Empire to the North Germanic lands. Their intention may not be this time to topple governments but find welfare. Just as the barbarians sought during the Era of Great Migration.