This is the classic work by Matthew Josephson on the famous monopolists of the nineteenth century: Carnegie, Rockefeller, Gould, etc. I'm a real fan of popular history like this (Cadillac Desert, for example), and this was no exception. Well told, and well organized. I quite enjoyed it.
One thing that stuck out for me was the diversity of attitude within the barons themselves. Jim Hill the railroad man was inclined toward engineering and built his roads solidly, while Jay Gould basically sucked the money and life out of anything he touched.
The work had a distinct Marxist character, which is typical for the time--1934, right in the midst of the Great Depression. Russia was on the upswing, and the last 140 years had been the worst kind of confirmation of Marx's historical predictions about capitalism. Still, Josephson keeps this kind of commentary to a minimum and focuses mostly on the gritty awful details of the barons.
Great work overall, highly recommended.