Until Mashiach comes, look at it this way: an Israelite/Jew (and every Israelite may be called a Jew because each Israelite is an acknowledgement of G-d) is someone born to a Jewish mother or who Halakhically converted. Everyone else is a non-Jew/non-Israelite/gentile/Noachide.
...just had another look at my first comment. It was vague and difficult to read. [g] Suffice to say that I don’t believe those who say that they are the “lost tribes,” and the explanation in your comment is all that is needed. Thank you for the mention of King Yoshiyahu (for study).
To be more clear on the part about the Shoah, could it be that the Nazis and others made their own evil decisions? They exhibited emotion with little intellect in order to murder and intellect with little emotion to rationalize their horrible deeds in wordy documents.
But then I’m still very new to study of the Oral. How much slack are we (all) given to decide as to what right or wrong thing we’re going to do next?