In a preventive war scenario, the rising state (the one that is becoming more powerful) would like to guarantee that it would not use its powerful position to exploit the declining state in the future. The declining state would like to accept such a guarantee. Both states would prefer such a guarantee to risky and costly fighting. Yet both states know that the guarantee would be worthless once the rising state achieves a dominant position. Hence, the declining state may launch a war now in order to avoid being exploited in the future.
Matthew Adam Kocher, Commitment Problems and Preventive War, 8 August 2013
Complete-information bargaining can break down in this setting if the shift in the distribution of power is sufficiently large and rapid. To see why, consider the situation confronting a temporarily weak bargainer who expects to be stronger in the future (that is, the amount that this bargainer can lock in will increase). In order to avoid the inefficient use of power, this bargainer must buy off its temporarily strong adversary. To do this, the weaker party must promise the stronger at least as much of the flow as the latter can lock in. But when the once-weak bargainer becomes stronger, it may want to exploit its better bargaining position and renege on the promised transfer. Indeed, if the shift in the distribution of power is sufficiently large and rapid, the once-weak bargainer is certain to want to renege. Foreseeing this, the temporarily strong adversary uses it power to lock in a higher payoff while it still has the chance.
Robert Powell (2006). War as a Commitment Problem. International Organization, 60(1), 169-203. doi:10.1017/S0020818306060061
Added to diary 15 March 2018