Surrendering hegemony collapses the nuclear umbrella---extinction from prolif.

The second problem with retrenchment involves nuclear proliferation. If the United States pulled out of NATO or ended its alliance with Japan, as many realist advocates of retrenchment recommend, some of its allies, no longer protected by the U.S. nuclear umbrella, would be tempted to acquire nuclear weapons of their own. Unlike the progressives for retrenchment, the realists are comfortable with that result, since they see deterrence as a stabilizing force. Most Americans are not so sanguine, and rightly so. There are good reasons to worry about nuclear proliferation: nuclear materials could end up in the hands of terrorists, states with less experience might be more prone to nuclear accidents, and nuclear powers in close proximity have shorter response times and thus conflicts among them have a greater chance of spiraling into escalation.