Why Football is part of American culture?

Since I came to American, I found American are crazy about football. I can see football every where. People watch football in cafe or thier dorm. They wear their teams cloths when their team are goiong to have a game. Football is party of their life.
Why American are so crazy about football? First, I think American like things which  big, loud, and strong. The football player are big strong and when they playing football they run very quick and hit each other very hard.  Second, football maybe a tool for American to communicate beacuse people who like the same time is easy to get together and make friends.

For these two reason, I thinking that's why American are so crazy about football.