Almost everything today feels like it is owned by eight or ten major parent companies. What changed to make the United States go from Anti-Corporate philosophies in the 1890s-1910s during Theodore Roosevelt’s “Trust Busting” era to lead to the modern economic practices?
While more can always be said, especially on a topic as complicated as this one, the answer here by /u/blue_ridge addresses the question (be sure to look at the second follow-up answer).