This study extends recent research on the power transition and hegemonic stability theory to the preindustrial era. It improves on the original power transition theory by relaxing an assumption and by extending the empirical domain. Unlike the original power transition theory, the revised version is not restricted to the period after the industrial revolution and can therefore be applied to the preindustrial era. This study examines the empirical record prior to the industrial revolution to see whether the power transition and hegemonic stability theory holds for that period. The data for 1648 to 1815 indicate strong support for the power transition contention that a rough equality of power between rival sides increases the likelihood of war. That is, when the challenging great power, with its allies' support, catches up with the dominant power, great power war is most likely.