"Why not we build a glorious city and a magnificent tower that reaches the heaven?"
"Good idea!". "Splendid!". "Yay!". The reason they could agree with each other was because they all spoke the same language.
They could all work together and they started building the tower.
God was unhappy about the people becoming arrogant and decided to destroy the project by confusing their language.
"Give me a brick!", one person would say but another person gave him a hammer.
"Give me a drink", one person would say but another person gave him a brick.
They realized they could not work together anymore and those that spoke the same language went away as a group.They quit building the city and ended up all over the world.
It became known as Tower of Babel because God made everyone at that time sound like babbling to each other.