Why are the green bay packers world champions if they only play in the usa?

It is because the NFL is considered to be the best football league in the world. The best football players play in the NFL. There are Canadian and European leagues of football but they are second tier compared to NFL. Therefore, if you win the Super Bowl you are considered the best team in the world-- its umed that the NFL is supreme to all of the other football leagues. You can compare it to saying "Well, why don't the NFL teams have to beat the NCAA champion to be considered world champions?" That's because NCAA is below NFL in terms of professionalism and eliteness. The same can be said for MLB Baseball and the World Series and the NBA and the NBA Finals. The best teams and the best players compete in those leagues.