All people on the earth had one language and the same words.
References for Genesis 11:1
When they traveled east, they found a valley in the land of Shinar and settled there.
References for Genesis 11:2
They said to each other, "Come, let's make bricks and bake them hard." They used bricks for stones and asphalt for mortar.
They said, "Come, let's build for ourselves a city and a tower with its top in the sky, and let's make a name for ourselves so that we won't be dispersed over all the earth."
Then the LORD came down to see the city and the tower that the humans built.
And the LORD said, "There is now one people and they all have one language. This is what they have begun to do, and now all that they plan to do will be possible for them.
Come, let's go down and mix up their language there so they won't understand each other's language."
Then the LORD dispersed them from there over all of the earth, and they stopped building the city.
Therefore, it is named Babel, because there the LORD mixed up the language of all the earth; and from there the LORD dispersed them over all the earth.
References for Genesis 11:9