Psst. Behind you.
The Kingdoms of Spain stopped having geography-centric units during the time of their Catholic Majesties’ reign; units would have many people from a given area only if that area happened to be where they’d been the last time they’d recruited (which could be the time the unit got created, of course - but later they’d get recruits from wherever). Mainly we had geography-based units for as long as they were led by their own liege lords.
Well, the geographically-based army unit formed, partially funded, and led by a local “lord” (factory owner, merchant, major landowner, etc.) lasted into the American Civil War. 
If memory serves, specific units were disbanded after the Christmas truce in WW1 on both sides, but that was before the Yanks arrived.
No, looks like the 1st ID stayed active.
Also, “disbanding” is (probably) technically different than deactivated. The U.S. military deactivates and re-activates units on a fairly regular basis; so often, in fact, that for an outside amateur historian observer like myself, I’ve never once understood how the heck people keep the Army regimental/divisional lineages straight.
I think here in 2012 there are only a few military units that are effectively immune from deactivation (I can’t imagine the 82nd and 101st being deactivated, for instance).
I find it horribly embarrassing that I can’t even sort out the tree of military groups very well - I have the vaguest notion of what platoons, regiments, divisions, armies etc. are but no more. So the history of specific groups… pfffft.
That would imply the UK did it more than all other countries put together, which is not in evidence. I’ll contend that’s not so, Germany doing it for their entire army would immediately rule out “mostly” as their army was larger than the UKs.