Up until the tower of Babel, the whole world knew of God - and there were no Jews until Abraham (that means everyone that was saved prior to that time were Gentiles - in the OT we see many Gentiles getting saved, including Ruth, Nebuchadnezzar, the whole city of Nineveh).

There are various places in the Bible where God teaches if someone searches for Him, He will reveal Himself - ie. He has obligated Himself to bring them the Gospel, so it does not matter their background. Their conscience and creation reveals there is a God/Creator - and if they truly search for Him He will reveal Himself to them.