<<A state of open, armed, often prolonged conflict carried on between nations, states, or parties.>>

If I might add a little pepper to the wurst. I believe, Cap (and perhaps just for the sake of being contentious) you have been seduced by the apparent meaning of the definition. The hint is in the "or," which is not exclusive and the answer is that the United States and Osama might each be party to a single conflict. According to the AHD, this need only be prolonged--whatever that means--et voila!