Some of the ancient sources thought this meant that Nimrod behaved in a high and mighty way, the first human being to do so.
According to Radak (David Kimchi), Nimrod was the first to impose himself on a nation as their king.
Until then, every people had its judges, but there were no political leaders. Nimrod was thus the founder of the idea of government.
In Radak’s view, this was not a bad thing; indeed, the Perek reflects that without government, people would “eat each other alive” (Avot 3:2).
Abravanel, who was a great advocate of republicanism, preferred to believe that Nimrod had forced himself upon the people, established the principle that monarchy goes with tyranny, and built great edifices to big-note himself.
Though Jewish thinking tends to prefer republicanism, our experience is that not all monarchs are bad and not all republics are good.
The great advantage of a republic is however that any citizen can become part of the ruling team, at least in theory, and a ruler is not there by divine right but because his people have elected him and can remove him.