World Football League (1974-1975)

Gary Davidson successfully founded the American Basketball Assn. and the World Hockey Assn. Yet his WFL ran up an estimated $20 million in debt and folded before the end of its second year.

U.S. Football League (1983-1985)

While the USFL introduced the two-point conversion (and Reggie White to the pros), it was undermined by an owner, Donald Trump, who insisted on scheduling the season to overlap with the NFL's.

World League of American Football (1991-1992)

Started by the NFL to promote football abroad, the WLAF led to the NFL Europe. Its final incarnation, NFL Europa, was disbanded in 2007. By then the league was losing $30 million a year.

Canadian Football League: U.S. expansion (1993-1995)

After the debut of its Sacramento team in 1993, the CFL created franchises in Las Vegas, Baltimore, and elsewhere. By 1995, however, all the U.S. teams had folded or relocated north.

XFL (2001-2001)

Founded by World Wrestling Entertainment Chairman Vince McMahon and NBC, the XFL held a championship game that was, at the time, the lowest-watched major network broadcast in prime time.