The story of the unfinished tower continues themes from the Table of Nations (chapter 10). These themes include language and human unity. The builders wanted independence from God, which recalls the rebellion in the garden of Eden (chapter 3). This also helps show why Abram’s faithful response to God is needed (chapter 12) during a time of disorder among the nations.
The scattering of the nations also points forward to later warnings given to Israel. God warned that idolatry would lead to their being scattered, and that their cities would be ruined (see Leviticus 26:33; Numbers 10:35; Deuteronomy 4:27; 28:64; 30:3).
In the timeline of Genesis, this goes back to an earlier time. It explains how the nations spread out during the time of Peleg (see Genesis 10:25).