"Yeah..." Shephard runs a hand over his face. "Far as I c'n tell, all the others still fit to hold a gun or stand on two feet got killed or worse by the Combine. There might not be a whole lot of country left to defend any more, but fuck me if I'm gonna let that stop me from doin' it the only way I know how. 'Sides, I got orders. I ain't allowed to die until I've passed on all the history'n tradition to a whole 'nother couple generations of Marines."

He's only about half joking. When Captain America- any Captain America, including the time-lost version known as Rojhaz- gives you the order to do something before you die, you don't die until you've done that thing.