The whole world had only one language. All people spoke it.
References for Genesis 11:1
They moved to the east and found a broad valley in Babylonia. There they settled down.
They said to each other, "Come. Let's make bricks and bake them well." They used bricks instead of stones. They used tar to hold the bricks together.
Then they said, "Come. Let's build a city for ourselves. Let's build a tower that reaches to the sky. We'll make a name for ourselves. Then we won't be scattered over the face of the whole earth."
But the LORD came down to see the city and the tower the people were building.
The LORD said, "They are one people. And all of them speak the same language. That is why they can do this. Now they will be able to do anything they plan to.
Come. Let us go down and mix up their language. Then they will not understand each other."
So the LORD scattered them from there over the whole earth. And they stopped building the city.
The LORD mixed up the language of the whole world there. That's why the city was named Babel. From there the LORD scattered them over the face of the whole earth.