"In 1965 the ratio of divestitures to acquisition and mergers was about one to eleven. By 1969 the number of acquisitions and mergers had soared above 6,000, and the ratio was a little more than one to eight. But by 1970 it was one to two and a half. For the years 1974 through 1977 there was one divestiture to every two mergers and acquisitions." (Chandler, Strategy & Structure)
Divestiture is a counterpart to M&As that certainly deserves much more thorough consideration. Who divests, when and why? Chandler attributes divestiture to "lose of competence" among managers. However, the number of M&As was always out-numbering divestitures. I doubt it was a case of poor managers having to let go of divisions that were picked up by skilled managers. There is a much richer story here.