I was at Time Warner when AOL bought us (one of the largest M&A deals ever). A disaster where the vast majority of the problem was the failure in realizing how different the cultures were and how much time and leadership it would take create a new pluralistic culture. Decision making, motivation and leadership style clashes caused massive confusion as well as differing business model where eyeballs were more valuable that product consumption, which lead to a series of initiatives harmful to Time Warner very corporate brands — Something as simple as converting from Outlook to AOL as our email systems was so disruptive. Making well established brands look like a start up.
Aside from the culture TW executive stock options were underwater after a couple quarter with no chance of recovering during those execs tenure.
We quickly cycle through the new leadership team, which were largely AOL folks plus the original CEO of TW.