We document a strong decline in corporate-diversification activity since the late 1970s, and we develop a dynamic model that explains this pattern, both qualitatively and quantitatively. The key feature of the model is that synergies endogenously decline with technological specialization, leading to fewer diversified firms in equilibrium. The model further predicts that segments inside a conglomerate should become more related over time, which is consistent with the data. Finally, the calibrated model also matches other empirical magnitudes well: output growth rate, market-to-book ratios, diversification discount, frequency and returns of diversifying mergers, and frequency of refocusing activity.

ABSTRACT We use panel data on S&P 1500 companies to identify external network connections between directors and CEOs. We find that firms with more powerful CEOs are more likely to appoint directors with ties to the CEO. Using changes in board composition due to director death and retirement for identification, we find that CEO‐director ties reduce firm value, particularly in the absence of other governance mechanisms to substitute for board oversight. Moreover, firms with more CEO‐director ties engage in more value‐destroying acquisitions. Overall, our results suggest that network ties with the CEO weaken the intensity of board monitoring.