Switching sides: changing power, alliance choices and US-China-Russia relations

How should alliance patterns respond to changing relative power? If states ally against the greatest threat, they should switch alliances if a shift in relative power makes a new state more threatening than the previous adversary. For some states, a "threat transition" will occur when the risk of a preventive war from the declining state falls below the risk of a revisionist war from the rising state, prompting a switch from the rising to the declining state. Such a threat transition may occur before, after or even in the absence of a power transition, in which the second-ranked state overtakes the most powerful state in the system. I present a model of alliance choice over time with changing relative power that develops the dynamic balance of threat perspective. I then discuss US-Chinese-Russian relations as an illustration of the model.