Much of the existing formal work on war models the decision to go to war as a game-ending, costly lottery. This article relaxes this assumption by treating war as a costly process during which the states run the risk of military collapse. The model also allows for uncertainty over either the cost of fighting or the distribution of power. The analysis makes four contributions to the growing costly-process literature: (i) the present model provides a more general treatment of the learning process that occurs when states are uncertain about the distribution of power, (ii) it explicitly compares the bargaining and learning processes for the two different sources of uncertainty, (iii) it suggests a way to empirically distinguish wars arising from these two sources, and (iv) it shows that the equilibrium dynamics of informational accounts of war may be quite sensitive to the underlying bargaining environment through which information is conveyed.