B) I can almost guarantee that there was state policies in play that aided in the formation of these oligopoly's as well; such as, the issuance of licenses and contracts to firms with connections within government.
They funded the construction of the rail road, and they gave Southern Pacific 175 million acres of free public land. The Pacific Rail Act had very little to do with regulation and everything to do with granting a state sponsored monopoly to Southern Pacific.And the government regulation which occurred in the railroad industry was mostly an optimization/safety standard than it was a "propping up" of a monopoly.
There were always competitors. Even Carnegie and later U.S. Steel had local competition in the form of J&L Steel.Steel had it's own regional monopolies as well.