Four Thousand years ago, Abraham (a great-great grandson of Shem, a son of Noah ) and a small group of Hebrews (of which there were & are many varieties) migrated from southern Iraq to Canaan (~Palestine). Several generations later, around 1853 BC, his Grandson Jacob (who was renamed Israel) and his 12 Sons and families moved to Egypt. As offspring of Shem, they were called "Shemites" or "Semites ", as were his many other offspring.
~1453 BC, now as the 12 Tribes of the 12 Sons of Israel, and over 3 Million strong, these Semites bailed out of Egypt in the well-documented EXODUS and fled back to ~Palestine. But the Tribes “couldn't all get along” there, so ~922 BC these 5 Million Israelites split into the Northern and Southern Kingdoms.
(In actual numbers, 5 Million people is about the same size as Ireland, Norway, Denmark or Israel today, and was 10% of the estimated 50 Million world population at that time. The world population is now ONE HUNDRED TIMES as large. Compared to todays 6 Billion people, the Israelites relative population would have been over twice as large as the United States of America!)
The very large Northern Kingdom of Israel was made up of 10 of the Tribes. Inheriting the Kingly names which applied to all 12 Tribes before the split, the Northern Kingdom (alone) becomes known as the Kingdom of Israel or House of Israel, (also House of Joseph, House of Ephriam, House of Isaac, and House of Omri), and is led by the northern Tribe of Ephraim.
Two hundred years later these Northern Israelites were taken into captivity by the Assyrians (~722 BC) and relocated to the northern Fertile Crescent area of Iraq/Iran. They were not diligent in updating their eMail addresses, thus were called, by some, the "Lost Tribes", or "Lost Sheep" or "Lost Children" of the Kingdom or House of Israel. (However at ~1/12 or more of the worlds population it seems unlikely they would actually disappear, or get "lost". The global population now ~75 Million.)
A hundred years later, this "lost" Northern Kingdom of Israel with now over 6 Million Israelites helped the Medes and Persians overthrow the Assyrians, then escaped north through the Caucasus Mountains and past the Black and Caspian Seas, to explode into history ~610 BC as The Celts . These Celts mixed with (and fought against) each other, and other scattered Israelites (proto-Celts) who had escaped from Egypt by sea a thousand years earlier, before the Exodus, and other Israelites who migrated from Palestine after the Egyptian Exodus but before the Assyrian captivity and who established numerous outposts in Europe and elsewhere.
These Millions of Celts grew to become Tens, then Hundreds of Millions as they migrated in waves westward and northwest to Galatia, Ephesus, Collosse, Corinth, Thessalonika, Phillipi, to what is today Hallstadt, Austria and Neuchatel, Switzerland (where exist major Celtic digs and museums) and beyond, to totally dominate Northern and Western Europe. These Celts (also as Cimmerians, Scythians, Danaoi, Massagetae, Milesians, Masilia, Sarmatians, Germani, Goths, Franks, Gauls, Lombards, Belgae, Angles, Saxons, Jutes, Vandals, Danes, Normans, and other assorted "Barbarians") are the rootstock of today’s Europeans and Americans who became the backbone of global Christianity .
The much smaller Southern Kingdom was made up of the Tribe of Judah & a mix of Levites and Benjamites. It was also known as the Kingdom of Judah or House of Judah. These Southern Israelites (aka Judeans) were taken captive in ~587 BC and removed to Babylon. Only ~50,000 Judeans returned to Palestine ~70 years later. They and their offspring are called Jews.