Trade union mergers have become common throughout the industrial world. In the United States, since the late 1970s, these have become increasingly multi-jurisdictional. Beginning in the 1990s, the trend has been dominated by five 'conglomerate' unions, who have embraced this as a strategy for growth and increased effectiveness. This article will examine the roots of this 'conglomerate' direction and quantitatively assess the claims for greater effectiveness in finances, organizing, and collective bargaining. The tentative conclusion is that while resources and policy matter, the conglomerate merger strategy of these unions has not improved any of these functions either over time or in comparison to other unions that have put less emphasis on multi-jurisdictional mergers.