I'd be reluctant to call the lords from the feudal system "oligarchs". Really, the people currently called such could only exist in a globalized economy.

But anyway, oligarchs weren't this powerful in the mid-century. FDR's New Deal was successful in bringing down the Robber Barons and ushering in America's golden age. Coincidentally, things started to go to shit with the introduction of Reaganomics and the promise that letting a few private individuals concentrate more and more wealth would be beneficial to the economy.