The analytic question is whether there is an option of unilateralism versus multilateralism, and secondarily whether it is available to all states or is only the luxury of a hegemonic power such as the US.
I want to argue what may seem to be two contradictory points. First, there is a sense in which multilateralism is an existential reality. And second, to the extant that unilateralism is an option, it is one available to all states and not just to a hegemonic US.
1) It is possible to argue that multilateralism is an existential reality.
This is akin to the argument made in the security literature that deterrence is an existential reality and not a doctrinal choice. However much governments procure weapons and espouse doctrines to the contrary, deterrence is simply a fact of life, one which constrains nuclear states.
The same point can be made about multilateralism. It is an existential reality. Much as governments try to deny the reality, much as they try to go it alone, they are in the end constrained by the reality that little of any consequence can be accomplished without acting in conjunction with important others. One can say that this lesson has even been learned by the Bush administration. Blowing things up is something the US can accomplish on its own (though even there it needs others’ approval for the use of overseas bases and for overflight permissions), but little else. In one domain after another, the US is looking for the support of others and has discovered this hard reality of international politics.
2) Unilateralism is open to one and all.
On the other hand, states do have a choice, and the choice of going it alone, separate from its efficacy and advisability, is open to all.
Think of the list of particulars used against the current US administration as evidence of its unilateral proclivities and ask how many of these steps are open only to a hegemonic power. Could Canada not decide to leave Kyoto? Could Canada have decided not to join the ICC? The consequences of joining or not may be different (both for the country and for all other countries), but the choice remains.
The same is true for the use of force. Take the case of Australia. It has militarily intervened twice in East Timor, once at the request of the international community and once at the request of the East Timorese government (I think I’ve got this right). The point, however, is that Australia has the ability to intervene militarily in its region and in line with its interests, and can do so even if it does not obtain Security Council approval.
The issues for any middle power are capability and cost. A state has the choice of acting on its own if it has the capability to do so and is willing to bear the cost. Israel chose to attack the Osirak reactor in Iraq in 1981. It had the ability and it was willing to pay the political costs of going ahead.
Unilateralism is more consequential the more powerful the state exercising it. A middle power pursuing a unilateral course can be seen benignly as a free rider or malevolently as a system challenger. But a hegemon pursuing unilateralism is likely upsetting the very possibility of a cooperative solution.