I think a migration era POD is the best course. Possibly, in the aftermath of Atilla's empire, a local warlord unites the Baltic peoples (lets make him Prussian, because: well, the Old Prussians need to get some proper attention on occasion!). The King begins to take advantage of the power vacuum and expands his realm over the Slavic peoples to the South. Although it takes a few generations (and lord knows there is infighting. You got to have in-fighting), the *Kingdom of Prussia encompasses all of the modern day Baltic territories as well as Poland and some of the *Eastern Slavic lands. Luckily, this is a tribal society and the dynasty is willing to accept the support of people, no matter what language they speak or gods they worship. Still its in everyone's best interest to learn Prussian and slowly the lands begin to Prussianize.
The dynasty founds a small city in OTL Gdansk and that city quickly grows due to royal patronage and comes to control the trade on the Baltic Sea. Although certainly no Rome or even Paris, is the largest urban center in Central and Eastern Europe at the time.
Now, eventually the Franks make contact with the Prussians and, at first, nothing much happens. But eventually the Franks get their Charlemagne-like figure and he seeks to gain the fealty of the Prussians. However his army is routed in battle and the two realms enter into a somewhat hesitant peace. The Prussian Kingdom begins to trade more with the West and knowledge and wealth go both ways. In the 9th century, feeling pressure from the Norse to the North and Slavs to the East, the Prussian King converts to Catholicism. *Gdansk is made the seat of a Bishop.
The Prussians weather the storm of the Norse, they secure their borders to the East. The Kingdom falls apart once or twice due to dynastic squabbling, but always manages to reunite in the end. It is a Prussian King who puts an end to the threat of the Magyars to the South - he forces the Magyar King to convert to Christianity, allows that King to marry one of his younger daughters. *Hungary becomes a client state to Prussia and, although it never becomes fully Baltic in culture nor custom, it is eventually annexed due to a dynastic inheritance. By the 15th century, the Kingdom (or, Empire, some are calling it) of Prussia is the undisputed master of Eastern Europe. It has pushed back the tide of the Slavs to the East and Prussian settlers are migrating into the OTL Ukraine to help found cities ...
How does that work?
The dynasty founds a small city in OTL Gdansk and that city quickly grows due to royal patronage and comes to control the trade on the Baltic Sea. Although certainly no Rome or even Paris, is the largest urban center in Central and Eastern Europe at the time.
Now, eventually the Franks make contact with the Prussians and, at first, nothing much happens. But eventually the Franks get their Charlemagne-like figure and he seeks to gain the fealty of the Prussians. However his army is routed in battle and the two realms enter into a somewhat hesitant peace. The Prussian Kingdom begins to trade more with the West and knowledge and wealth go both ways. In the 9th century, feeling pressure from the Norse to the North and Slavs to the East, the Prussian King converts to Catholicism. *Gdansk is made the seat of a Bishop.
The Prussians weather the storm of the Norse, they secure their borders to the East. The Kingdom falls apart once or twice due to dynastic squabbling, but always manages to reunite in the end. It is a Prussian King who puts an end to the threat of the Magyars to the South - he forces the Magyar King to convert to Christianity, allows that King to marry one of his younger daughters. *Hungary becomes a client state to Prussia and, although it never becomes fully Baltic in culture nor custom, it is eventually annexed due to a dynastic inheritance. By the 15th century, the Kingdom (or, Empire, some are calling it) of Prussia is the undisputed master of Eastern Europe. It has pushed back the tide of the Slavs to the East and Prussian settlers are migrating into the OTL Ukraine to help found cities ...
How does that work?