Was Israel the only nation that knew the one true God when they came on the scene?
Yes. When Israel emerged as God's separated covenant people, Scripture and history indicate they alone knew the one true God. The rest of the populated world—every human being outside Abraham, Isaac, and Jacob—was steeped in paganism and polytheism, worshiping many gods.
Les explains that ever since the Tower of Babel, the whole human race until Abraham was saturated in paganism and polytheism—the worship of many gods. When Israel comes on the scene as His separated, different covenant people, they are the only people on earth. The populated world around the Mediterranean, on into the Middle East, and maybe out to China was pagan, but Israel alone was that little group, that little nation, with a knowledge of the one true God. Les also notes the natural question: why didn't God send the Jew out into those pagans to enlighten them?