[David1]

Remember, the US is working on a space-based laser constellation that will be aimed at destroying a missile on its boost phase. The boost phase is the phase where the missile is more vulnerable because it would be rising up against gravity. At this stage, it would be very vulnerable from laser attack and MIRV will not work in this stage. Plus, the attacking country would be going against the risk that the destroyed missile would be dropping back over its own territory which would give an attacking country even more pause.
You can read more here:
http://www.globalsecurity.org/space/systems/sbl.htm
and
http://www.acq.osd.mil/bmdo/

[Filibuster_60]

At this point the Space Based Laser is clearly still in the research stage. I don't think it'll be ready before the Airborne Laser, and the ABL itself might have to wait until 2010. Granted, it's the best defense against emerging ballistic missile threats, but supposing it enters service in the 2020-2025 timeframe, the bigger powers will have had plenty of time to work on countermeasures. I don't expect today's ICBM technology to be militarily useful in 2020.

Control of space will be key to control of the ground in 21st-century warfare, and all the major powers are aware of it, but how soon, if ever, space weapons render all land-based missiles obsolete is anyone's guess. Major technical hurdles must be overcome. The biggest issue at present is how to generate sufficient energy to ensure a kill. It might have to be done with nuclear power.

As it is I don't expect the US to have a total monopoly in space. Unfortunately we've already wasted plenty of time and money so that the gap between us and the other big powers isn't as big as it could have been.