an iranian supply route for u.s. forces will never happen, but based on geography alone, it's the only option other than through pakistan that makes any sense.
a few weeks ago, the pentagon was floating a bunch of alternatives that traveled through various republics of the former soviet union. but they all seemed pretty convoluted if you're familiar with the geography. the area that once was the soviet union isn't one big country anymore. the favored route seems to go from estonia, to russia, to kazakhstan, to uzbekistan. but if you go with that one you're giving four different countries an effective veto over the u.s.' supply lines. you can fiddle with the route a little bit, knock out uzbekistan and replace it with kyrgyzstan and tajikistan, but that increases the number of potential vetoes to five. you could also replace uzbekistan with turkmenistan, that would keep it to four, but turkmenistan has been the least supportive of the afghan operation of any of the central asian republics from the beginning. then again, kyrgyzstan is in the process of kicking the u.s. out of its bases and uzbekistan already did that in 2005, so there are problems no matter which one you choose. plus four to five potential vetoes is just asking for problems. and however you do it, both russia and kazakhstan will get one.
if you want to minimize the number of countries involved (and thus the potential for disruptions when political differences arise) the best overland route from international waters to afghanistan is either through pakistan or iran. that's putting aside politics. which, of course, you can't really do. i just don't see any good options if you're looking for an alternative to pakistan.
