Umm ... since US Steel is still around, when was it broken up? "Not surprisingly, U.S. Steel was prosecuted for violating antitrust laws. It escaped dissolution by only one vote in the U.S. Supreme Court." (http://www.businessweek.com/2000/00_35/b3696013.htm)
Thankyou Captian History. US Steel was not forcibly demonompolized because the company agreed to do it on his own. After forming a near monopoly be merging and acquiring 11 companies in 1901, the company backed out of acquiring Bethlehem Steel in 1904. Why? Beacuse of what was happening to Standard Oil. Bethlehem was a formidible competitor by the 1920's when the auto industry took off. Further antitrust legislation was enacted in the in the intervening period. The point is, there was no steel monopoly for the automakers to deal with, and it was because the federal government did not allow it. Period.