I think "pack leader of the U.S." is a notion from a different Urban Fantasy 'verse, not Dresden (Patricia Briggs' "Mercy Thompson" springs to mind, and I expect there are others (what about WW/WoD "Werewolf" RPG? ) ) . IMHO it works rather poorly with DF, because a "pack" seems to only be interested in the "territory" they can reasonably reach in their wolf-form in a relatively-short timespan (i.e. a rather "naturalistic" / instinctive wolf-view). I think a DF werewolf (of the kind the Alpha's are) would think it wierd, possibly ludicrous, to claim "pack territory" that's a week's journey away, let alone something only viably reached by aircraft... Each pack would see itself as entirely autonomous.
That said, I am very much against telling my players that something they want is BadWrongFun, so I'd look for a way to make it work. Others have already given some good suggestions. I'll add a notion...
Werewolves *ARE* intelligent, planning beings, and I can see that they may have found some need, at some point, for a very-large "multi-pack" association (maybe the U.S. Civil War?) -- and such an association may still exist, at some level. So far as I recall, we've never seen any hint of it in WoJ or DF canon, nor DFRPG sources (hint/pointer anyone?), so let's say it's somehow "inactive." It may be entirely theoretical, having been inactive for a century or more, with a titular "head werewolf" (the Alpha for the pack whose Alpha was the leader *last* time the "Pack USA" was active). Some pack Elders still recall the stories from that time, however.
Now there is *something* causing (some) werewolves to think that the Time Has Come to reactivate the UberPack. There may be mystics, prophetic dreams, Shamanic dream-quests, etc... Others think it's a bullshit move by power-hungry idjits (or cowardly weaklings seeking "protection") who have let their human weaknesses invade their wolf-selves, and long for nothing more than to rip the throat out of anyone who suggests such a thing...
Even amongst those who think the UberPack needs to come back, nobody can really agree *WHAT* the looming problem is... NOR do they all agree that the same pack's Alpha is just automatically the new UberAlpha, etc...