Since football championship games have been played in the NCAA (1992-1994 Bowl Coalition, 1995-1997 Bowl Alliance, 1998-present BCS) two teams from the same conference have never met for the national championship.
Yes, through the 2009 season that has occurred 16 times since the AFL-NFL merger in 1970:
1) 1971 - Miami Dolphins 21, Baltimore Colts 0 (AFC East)
2) 1972 - Washington Redskins 26, Dallas Cowboys 3 (NFC East)
3) 1977 - Denver Broncos 20, Oakland Raiders 17 (AFC West)
4) 1978 - Pittsburgh Steelers 34, Houston Oilers 5 (AFC Central)
5) 1979 - Pittsburgh Steelers 27, Houston Oilers 13 (AFC Central)
6) 1980 - Philadelphia Eagles 20, Dallas Cowboys 7 (NFC East)
7) 1980 - Oakland Raiders 34, San Diego Chargers 27 (AFC East)
8) 1982 - Washington Redskins 27, Dallas Cowboys 17 (NFC East)
9) 1982 - Miami Dolphins 14, New York Jets 0 (AFC East)
10) 1983 - Los Angeles Raiders 30, Seattle Seahawks 14 (AFC West)
11) 1985 - New England Patriots 31, Miami Dolphins 14 (AFC East)
12) 1986 - New York Giants 17, Washington Redskins 0 (NFC East)
13) 1989 - San Francisco 49ers 30, Los Angeles Rams 3 (NFC West)
14) 1992 - Buffalo Bills 29, Miami Dolphins 10 (AFC East)
15) 1999 - Tennessee Titans 33, Jacksonville Jaguars 14 (AFC Central)
16) 2008 - Pittsburgh Steelers 23, Baltimore Ravens 14 (AFC North)
Yes. In the 1996 season, Florida State and Florida played in the Sugar Bowl for the National Championship. I'm not sure about any other intra-state meetings.
Steelers and Eagles.
no
Army/Navy
They do, when the American League teams and the National League teams play each other.
Yes. Each season teams will play 15 to 18 games against teams from the other league.
It is the national sport of many countries, and because there are teams from many countries that play each other at many levels, it is an international sport.
No. They cannot play each other in the World Series as both teams are in the National League.
Its a abbreviation for the national football league. As there aren't any other leagues of football teams that compete constantly with each other to make money it must be a monopoly.
NBA Basketball is an association called the National Basketball Association. In it people play basketball in a season on one of the 30 teams. The teams verse each other at one of their home courts. (Each team has there own court with the team name painted in the middle.)
Four teams per division
Each team plays 46 games; the total for the season is 552.
English teams can face each other in the Champions league from the quarter finals stage. This is because after this stage, teams are drawn randomly to face each other.
The National Football League (NFL) has 32 teams. 2 Conferences (AFC and NFC) each of 16 teams, and each conference has 4 divisions (North South East West) and each division has 4 teams. Ex: The AFC East has 4 teams, New England Patriots, Miami Dolphins, New York Jets, and the Buffalo Bills
Starting in 2013 there will be 15 teams in each league (currently there are 16 in the National League and 14 in the American League but Houston will be moving to the AL starting next year). Because there are an odd number of teams, there will always be one team from each league that will have to play outside their league.