The industrial revolution began before the civil war; export-driven growth began taking off in the 1840s. More broadly, industrialization weakened an artisan middle class - wages fell during early industrialization. This power was always concentrated in the hands of a bourgeois owning class; the limited liability corporation was one of the key early innovations of American government in promoting this economic form.

The modern corporate form did not develop until later - a managerial class emerged starting around World War II (see: James Burnham) and is, I think, a big explanation for why the previous Gilded Age saw massive labor organizing that eventually drove American policy change, but this era has not - the ruling class bought their own organizers this time.