Are these critical differences not an iron law of our development?

It has to do with an iron law of economics.

The marriage had been forced upon her by the iron laws.

One need not try and turn this maxim into an iron law.

No doubt what's on his mind is the third iron law of cultural trends: the backlash.

But an iron law of American culture is that nothing once popular is ever gone forever.

The size and complexity of a group or organization is important to the Iron Law as well.

According to the "iron law," democracy and large-scale organization are incompatible.

And there were iron laws of tradition and law on four sides.

It appears an iron law: Kill a nation's faith, and its people will cease to reproduce.