> But chances are, almost none of those coming realises that [Philadelphia] was once part of a little-known Swedish colony known as Nya Sverige (New Sweden).

That's all it's trying to say in this sentence. It's not trying to say that the New Sweden colony was actually the US's political and ideological birthplace. (That's how you read it, right? I'm not sure how your last sentence makes sense otherwise; Philadelphia was a creation of the same European country as Virginia.)