Before 2009, Colin Kaepernick would have had to find some other way to protest racism against African Americans. That's because until the height of the Iraq War, NFL football players weren't even required to leave the locker room for the national anthem, much less stand for it.
That's not to say that the national anthem didn't take place before every game. The singing of "The Star Spangled Banner" was mandated during another war, World War II, when the NFL commissioner at the time mandated it for the league.
The players were told to stand for it about the same time that the Department of Defense was ramping up massive recruitment and media operations around the wars in Iraq and Afghanistan.
They began paying sports teams millions in U.S. tax dollars for what amounted to "paid patriotism," or mega-military spectacles on the playing field before the games. It got so bad that there was a congressional investigation led by none other than Sen. John McCain (R-Ariz.), a veteran and considered one of the most patriotic men in the Senate.