A simple, general mathematical model for modern war is presented. The form of the model is Lanchester but its derivation owes approximately equal amounts to classical operational research and to later ideas associated with theoretical ecology - especially the concept of 'carrying capacity'. Solutions to the equations corresponding to stalemated, steady-state outcomes in theatre are concentrated on, with empirical justification derived from the unduly neglected databased work of Voevodsky. Prolongation and stalemate are seen as the default state of modern war. War termination is discussed as a consequence of 'mutually (but not equally) hurting stalemate'. Examples are given of how, in certain circumstances, stalemate may be pre-empted in theatre by striking at non-battlefield targets and light is cast on the late 20th-century strategic trend towards conducting war preponderantly from the air.