Would have been possible to have established any powerful maritime city-states from anywhere between Ireland and Scandinavia? Places like Swedish trading centre of Birka located in Lake Malaren?
Don't see why not, Venice one of the major city states ended up owning large swathes of land inland and along the Adriatic coast. To keep it a true city state and from expanding into Ireland though you'd probably need some strongish neighbouring states to balance things out by being strong enough to avoid annexation themselves but weak enough to not be able to annex Dublin.Kingdom of Dublin might be considered city-states, its quite small.
Would have been possible to have established any powerful maritime city-states from anywhere between Ireland and Scandinavia? Places like Swedish trading centre of Birka located in Lake Malaren?
in the age of Vikings ? Vikings would certainly disturb trade, so it difficult to create city-states.
Kingdom of Dublin might be considered city-states, its quite small.
This is gonna require an early point of divergence. I'm thinking Roman times. The Scandinavians were pretty much savages up until the time period you're talking about. If you want maritime republics in Scandinavia by that point, you'll need to have the Romans come up there, colonize the place and then remaining there long enough to make a significant impact. Now, unless I am mistaken, Scandinavia does appear in Roman chronicles, so I guess you could start there. Them Roman Emperor weren't precisely the most rational actors, so you could very well have one of them decide to go North, as to speak. Once Western Rome collapses, a much earlier Christian civilization can then arise among the Roman ruins in Scandinavia.
That would be awesome.
I think its doable on the Scandinavian's own terms. By the 700-800's, the Norse were looking for places that could support their numbers better than the soil of their own homeland. They certainly need an early POD, but rather some regional centre would need to have an earlier stranglehold on outside trade before they begin colonising other parts of northern Europe. Maybe a century or two before the Viking Age. Then they could exert influence over the other Aettr of Scandinavia.