“Henges are only known to occur in Britain and Northern Ireland.”
I don’t think that’s correct. There are remains of henge in the Netherlands.
I think the circular layout is (nearly) unique to the British Isles; there are “Medicine Wheels” in North America, but the stones used are not enormous. The unexplained megalithic construction can be found all over the world, however, including the lines of stones at Carnac in Brittany.