The Welsh and the Celts are probably descended from Dan. They would've arrived in the British Isles in ships before the captivities. Then after the captivites, the British, who would have been of the tribes of Ephraim and Manasseh (mostly Ephraim) arrived after going across Europe in the great migrations. The Welsh and the British are cousins. Just like the British and the Jews are cousins, and therefore Americans and Jews, Americans being mostly of the tribe of Manasseh.