the Cleveland Browns and the San Francisco 49ers from the AAFC. A third AAFC team, the Baltimore Colts (not related to the 1953–1983 Baltimore Colts or to the current Indianapolis Colts franchise), played only one year in the NFL, disbanding at the end of the 1950 season. The league resulting from the merger was a 26-team juggernaut (since expanded to 32) with television rights covering all of the Big Three television networks and teams in close proximity to almost all of the top 40 metropolitan areas, a fact that has precluded any other competing league from gaining traction since the merger; failed attempts to mimic the AFL's success included the World Football League (1974–75), United States Football League (1983–85), the United Football League (2009–2012) and the AAF (2019), and two iterations of the XFL (2001 and 2020). The AFL was also the most successful of numerous upstart leagues of the 1960s and 1970s that attempted to challenge a major professional league's dominance. All nine teams that were in the AFL at the time the merger was agreed upon were accepted into the league intact (as was the tenth team added between the time of the merger's agreement and finalization), and none of the AFL's teams have ever folded. For comparison, the World Hockey Association (1972–79) managed to have four of its six remaining teams merged into the National Hockey League, which actually caused the older league to contract a franchise, but WHA teams were forced to disperse the majority of their rosters and restart as expansion teams. The merged WHA teams were also not financially sound (in large part from the hefty expansion fees the NHL imposed on them), and three of the four were forced to relocate within 20 years. Like the WHA, The American Basketball Association (1967–76) also managed to have only four of its teams merged into the National Basketball Association, and the rest of the league was forced to fold. Both the WHA and ABA lost several teams to financial insolvency over the course of their existences. The Continental League, a proposed third league for Major League Baseball that was to begin play in 1961, never played a single game, largely because MLB responded to the proposal by expanding to four of that league's proposed cities. Historically, the only other professional sports league in the United States to exhibit a comparable level of franchise stability from