Almost but not quite - British Israelism believers believe the Jews are indeed Jewish, but that the "ten lost tribes" (i.e. the descendants of the other sons of Israel that didn't become Jews and faded out of history) cruised over to Northern Europe. Brits are of Ephraim (Joseph's son), which would then extend to Americans too. Not sure if/how Manasseh fits
You've then got Nordic Israelism which emerged a little later as an add-on to the above. Finns are of Issachar (because the word for father in Finnish is Isa), Dan became the Danes and Icelanders are somehow connected to Benjamin for reasons I don't quite understand (also considering that in the bible itself the tribe of Benjamin splits from Israel with Judah to make the kingdom of Judaea, Benjaminites would have been absorbed into modern Jewry).
In the deeper theories of Black Hebrew Israelism, your tribe depends on where your ancestors were dumped as slaves in the Americas. Somehow if you originated from the same place in Africa but landed in the US vs landing in Jamaica you are two different tribes. I'm not sure how many BHI hold to this belief now.
Pic 1 Pic 2
Honorable mention to the Mormon explanation of why there are native Americans - descendants of a bunch of Israelites who moved to America and turned against their God-fearing brethren. As punishment God turned their skin red from the previous "white and delightsome" (actual quote from the book of mormon that has since been revised to "pure and delightful" in the late 20th Century). Black people exist because they chose neutrality in the war between good and evil before being born on earth so that's their curse (those on team Jesus became white people. Satan's buddies became demons). Gross oversimplification, but they are now embarrassed by this theology and keep it on the down-low and show off how diverse their churches are.
Here's a cute cartoon explaining it all, though I don't care to check how accurate it is.