The NFL operated in a two conference system
From 1920 to 1934, the NFL did not have a set number of games for teams to play, instead setting a minimum. The league mandated a 12-game regular season for each team beginning in 1935, later shortening this to 11 games in 1937 and 10 games in 1943, mainly due to World War II. After the war ended, the number of games returned to 11 games in 1946 and to 12 in 1947. The NFL went to a 14-game schedule in 1961, which it retained until switching to the current 16-game schedule in 1978. Proposals to increase the regular season to 18 games have been made, but have been rejected in labor negotiations with the National Football League Players Association NFL Coins.
The NFL operated in a two-conference system from 1933 to 1966, where the champions of each conference would meet in the NFL Championship Game. If two teams tied for the conference lead, they would meet in a one-game playoff to determine the conference champion. In 1967, the NFL expanded from 15 teams to 16 teams. Instead of just evening out the conferences by adding the expansion New Orleans Saints to the seven-member Western Conference, the NFL realigned the conferences and split each into two four-team divisions. The four conference champions would meet in the NFL playoffs, a two-round playoff.The NFL also operated the Playoff Bowl (officially the Bert Bell Benefit Bowl) from 1960 to 1969. Effectively a third-place game, pitting the two conference runners-up against each other, the league considers Playoff Bowls to have been exhibitions rather than playoff games. The league discontinued the Playoff Bowl in 1970 due to its perception as a game for losers.
Following the addition of the former AFL teams into the NFL in 1970, the NFL split into two conferences with three divisions each. The expanded league, now with twenty-six teams,would also feature an expanded eight-team eight playoff, the participants being the three division champions from each conference as well as one 'wild card' team (the team with the best win percentage) from each conference. In 1978, the league added a second wild card team from each conference, bringing the total number of playoff teams to ten, and a further two wild card teams were added in 1990 to bring the total to twelve. When the NFL expanded to 32 teams in 2002, the league realigned, changing the division structure from three divisions in each conference to four divisions in each conference. As each division champion gets a playoff bid, the number of wild card teams from each conference dropped from three to two.