Question: How can you be certain that the 10 kingdoms are the European Federation? Could the world and its nations look significantly different 1000 years from now?
One of the reasons I love visiting Europe is for all the history. On my last trip, I visited Trier on the far west side of Germany. It has one of the largest city gates still standing, north of the Alps — the Porta Nigra — built for and used by the Romans throughout their reign. (That’s me, standing in front of it, in the picture.) I say this because, as Americans, our geography and our knowledge of history can be shoddy. The Roman Empire was not confined or even mainly in & around Italy. It was all across Europe. Great Britain was a major Roman province named Britannia, with Hadrian’s Wall blocking off access to the northern barbarians (the Scots).
So, yes, you can be certain that the 10 kingdoms are Europe. Not necessarily the European Union in its current state, for as you say, things can look significantly different over the span of years. But geographically, this does appear to be the region and people from which the 10 kings prophesied in Daniel 7 shall arise.