[Nomentatus]

It's a misconception that The Sherman Act was the beginning of the restraint on monopolies. It's more the other way 'round. Common law concerning restraint of trade goes back hundreds of years before, and could really pinch, with no limits on remedies. John Sherman's act LIMITED how much a railroad (etc) could be fined for it's misbehavior, rather than introducing a legal risk. That risk already existed under common law under the rubrik "restraint of trade" [1] and could be extremely potent, in the years before the Sherman Act existed. The advantage of a statute was that statutes overrule common law, sending the strong and expansive existing common law vs "restraint of trade" into the dustbin of history. To the great benefit of railroads, etc. It's relevant that his brother (General) William T. Sherman was the President of a (urban) railroad when the Civil War started. The Republican party (of John Sherman) was a strong proponent and friend of industry and infrastructure, not an enemy of it.

[1] https://en.wikipedia.org/wiki/Restraint_of_trade