"Then God blessed Noah and his sons, saying to them, 'Be fruitful and increase in number and fill the earth.'" (Genesis 9:1)
So God's command was for people to spread out and settle the whole earth. And what did they do?
"Now the whole world had one language and a common speech. As men moved eastward, they found a plain in Shinar and settled there. They said to each other, 'Come, let's make bricks and bake them thoroughly.' They used brick instead of stone, and tar for mortar. Then they said, 'Come, let us build ourselves a city, with a tower that reaches to the heavens, so that we may make a name for ourselves and not be scattered over the face of the whole earth.' But the Lord came down to see the city and the tower that the men were building. The Lord said, 'If as one people speaking the same language they have begun to do this, then nothing they plan to do will be impossible for them. Come, let us go down and confuse their language so they will not understand each other.' (Genesis 11:1-7).
They decided they had a better plan. They could accomplish more when they were united, so they banded together. Their purpose was diametrically opposed to what God had told them. He said "Spread out!" They said "Let's stick tight!" They started a massive building project whose purpose was completely humanistic: let's do this so "we may make a name for ourselves." We've got some good ol' secular humanists here!
"What has been will be again, what has been done will be done again; there is nothing new under the sun." (Ecclesiastes 1:9)
Hmmm... sounds like the human heart hasn't changed all that much over the years!
Why did God tell Noah's descendants to spread out? I don't know. But here's some ideas. Maybe He wanted the people to see the varied beauty of the world He'd created, beautiful even after a cataclysmic flood. Maybe He didn't want sin to be able to pass so rapidly through a concentrated society, like an infectious disease. Maybe He didn't want a centralized power structure, but a diffuse power structure.
Think about it. If the power over the whole earth was concentrated in the hands of one man or one ruling class, think of the temptation and power to abuse that he would have! Sure, there would be the greatest possibility for good, but at the same time, there would also be the greatest possibility for evil. Think of how Satan would attack and cajole him! Because if Satan could guide or coerce this man's decisions, he would rule the earth! And even aside from Satan's direct attacks, the man's own "bentness" would be enough to lead him into sin. Diffuse power, baby. That's the way to go! Divided powers, checks and balances!
Whatever His reason or reasons, God made it clear that he wanted people to spread out, not conglomerate.
Excited about a one-world government? Been there, done that. As far as it depends on you and me, let's not do it again.