Two features radically distinguish the Sherman Act from European competition law. First, its criminal dimension: a cartel can send an executive to prison. Second, the treble damages mechanism, which turns every victim into a private prosecutor and makes economically rational litigation that European law would leave unpursued.
The law does not prohibit every restraint of trade, but only unreasonable restraints — a nuance introduced by the case law as early as 1911. That is the origin of the fundamental distinction between practices that are illegal in themselves and those that must be weighed.
Its application to the labour market is recent and decisive: agreements between employers not to poach each other's employees are now analysed as cartels.