The issue was using conventional ICBM's. I did a quick research and found some old articles : ArmsControlWonk (August 2005), Aerospace Power Journal (Fall 2001), "abovetopsecret.com" (April 2007). I assume from these that conventional missiles is already an old tendency, and more the will of military people than politicians. Again, from RTI : globalsecuritynewswire. May be that they are exploiting the START treaty to get what they wanted since a couple of years. As for politics : New York Times. Both worries about antimissile systems and modernization are raised (not sure on the latter), while those conventional missiles don't seem to bother anyone. I must admit, I have been surprised to learn that MIRV had been slowly abandoned after Cold War. Now it's only a detail, impacting the effectiveness of missiles. If no one cares, then sounds good. On another note, is it really the treaty that prevents modernization ? Or is it a decision solely made by the DoD ? I didn't read the treaty itself.