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Copeland. 2000. The origins of major war. Ithaca: Cornell University Press.

I've got a nice PDF summary of this.

Copeland begins with a critique of three historical realist theories: classical realism, neorealism (Waltz), and hegemonic stability theory. He presents his new theory: dynamic differentials theory. This theory looks at how changing relative capabilities (i.e. "dynamic differentials") in military, economic, and potential power affect the probability of war. It's largely a revision of hegemonic stability theory.

THE VARIABLES AND PREDICTIONS:

Y = probability of war

Intervening variable: the state's selection of a policy response along the hard-line/soft-line spectrum.

X = Three variables about "dynamic differentials," three variables about the effects of any given policy.

The five possible policy responses along the hard-line/soft-line continuum (from hard to soft): (1) initiate war, (2) initiate a crisis, (3) deterrence/containment, (4) do nothing, (5) reassurance/accomodation.

X1, X2, X3: The three "dynamic differentials" variables:

1. Present differential of relative military power
2. Depth of dominant state's future decline in the absence of "strong" action
3. Probability of dominant state's decline in the absence of "strong" action

X4, X5, X6: The three parameters that affect how a state responds to these three "dynamic differentials":

1. "the extent to which hard-line policies . . . hold out the prospect of overcoming the state's decline"
2. "the extent to which such hard line actions will increase the probability of" inadvertent major war
3. "the probability of the other [state] attacking later" if it is allowed to continue to rise

Assumption: The declining state's objective is to "pick the option that maximizes the state's security, that is, the option which, all things considered, leads to the highest expected probability of survival (EPS) over the foreseeable future."

Main prediction: "All things being equal, the more severe a state's decline will be in the absence of strong action [X2, X3, X4], the more severe its actions are likely to be, that is, the more risks of inadvertent spiraling [X5] it will be willing to accept."

Two primary hypotheses:

1. "the greater the declining state's inferiority in economic power and potential power, the more likely it is to pursue risky policies"
2. "in multipolarity, the declining state will be more likely to initiate major wars or crises/cold wars that increase the risk of inadvertent major war when it possesses marked military superiority versus the other great powers taken individually"

FIVE PATHS TO WAR

1. Direct preventative attack (crisis is optional, has no independent role); declining state prefers war to peace
2. Declining state uses a crisis to justify an attack that it wanted to do anyway [Bush in Iraq?]
3. War happens after the declining state provokes a strategic crisis and then is forced to go through with the war to save face after the strategy fails, declining state prefers to fight than accept the status quo but is open to peaceful changes to the status quo
4. Preemptive attack because the declining state thinks another state will attack it, but prefers peace to war
5. Similar to (3) except that states prefer the status quo to fighting but given their provocative actions, prefer to fight so as not to appear weak in the future

TEST CASE (and inspiration for the theory): WWI. Germany took a series of deliberate steps to provoke a crisis that would lead to war with Russia (a rising power) and make it look like Russia's fault.