The shift to unipolarity has introduced new dilemmas for America's allies. Their level of strategic uncertainty has increased, largely because under unipolarity, allies' threat perceptions are more likely to diverge across time or issue areas and are not shaped as much by structural systemic factors. Although they want to maintain the pre-existing security arrangements as a means of managing the rising uncertainty, allies need to deal with the dual concern of either being trapped into the hegemonic partner's policies, or being abandoned by the hegemon. These two concerns - the alliance security dilemma - may become more or less prominent given the nature of the divergence in threat perceptions on different issues and at different times. To deal with this dual threat, allies employ two strategies: using the pre-existing alliance as a pact of restraint, and developing a division of labor with the hegemon. Both the dilemmas and the strategies used to mitigate them are examined here in the context of the European behavior within NATO following the Gulf War, the NATO involvement in Kosovo, the war in Afghanistan, and the war in Iraq.