The agreements are usually preceded by a player strike, and have been focused on topics such as player benefits, injury compensation, the sharing of league revenue, and many other areas in which the players felt like they were not being fully respected or helped.
The first ever CBA was created in 1968 when some players went on to strike to fight for increased pensions and a larger minimum salary. The was the first ever lockout as owners responded to the strike by not allowing these players to play, but eventually a deal was reached where rookies and veterans were given a larger minimum and more league revenue was set aside for pensions.
The most recent of the six CBA's since the labor agreement's inception was in 2011. This deal ended the NFL's longest ever lockout and focused on reducing the injury risk for players specifically in the offseason. The number of off-season workouts that could be held were decreased as well as the amount of full pad, full contact practices.
The current CBA is a 316-page document that outlines every aspect of the deal. The 2011 agreement is in effect through 2020, when the NFLPA will inevitably begin to advocate for changes that could lead to another strike at the end of that season.