It was the Apostle Paul who went to the Galatians in response to Jesus admonition in Matthew 10:6 (and elsewhere in Matthew) to "... go rather to the lost sheep of the house of Israel." Does that mean the Galatians were the Lost Sheep of the House of Israel???
Yes, and more.
The Lost Tribes of Israel, who were the old Northern Kingdom (aka the House of Israel), were the Galatians (and Corinthians, and Phillipians, and Ephesians, etc....), were Celts. They became the root stock of Europe and its colonies, including the United States of America.