Israel was once a nation of 12 tribes. Like the USA they had a rebellion. The northern 10 tribes rebelled against the southern remaining 2 tribes of Judah (where Jerusalem was) and Benjamin.
But unlike the USA, there was no civil war. Judah was about to fight, but God intervened. This breakaway was His doing. Soon the pagan northern tribes formed a separate nation. Samaria became their capital city. They had abandoned the temple of Jerusalem and worshiped idols in northern locations.
When I was recovering from my stroke, I stayed in a senior care facility. We had a very tall Ethiopian man as a waiter. He told people he was one of the ten lost tribes of Israel. This is still told today--the ten Lost Tribes.
Ethnically, the ten rebellious tribes may be anywhere today. The cult of Anglo-Israelism claims that they became Britain and the USA. But religiously, Israel is composed of the faithful of all twelve tribes.
After the rebellion under Solomon's son Rehoboam in about 980 B.C., these faithful ones left the northern kingdom and came back to the south. The Bible said they strengthened the Davidic kingdom. This is revealed in 2 Chronicles 11:13.
So it is that in 56 to 58 A.D., Paul said he was an Israelite of the tribe of Benjamin, a southern tribe. The unfaithful went north, the faithful resorted to the south. Religiously Israel was composed of 12 tribes once again.