With the break up of the Spanish empire in South America, the continent split into nine independent states with often ill-defined boundaries. One of these was that between Bolivia and Chile, which were separated by the Atacama Desert, tone of the driest regions in the world. When it was realised that the area contained nitrates that the world needed for explosives and fertiliser the scene was set for the inevitable clash. When war broke out in February 1879, both sides found themselves unprepared for war. Rapid armament followed as the Peruvians were dragged into the conflict in support of their Bolivian allies. Initially there was a tiresome naval war of blockade and guerre de course. Two naval actions decided the naval campaign in favour of the Chileans who then proceeded to use their naval power to attack the Allies' isolated armies and capture Lima two years after war had broken out. Fighting then developed into a cruel and ruthless guerrilla war in the Andes, sometimes even pitting Peruvian against Peruvian, before the Peruvians finally concede defeat. The war was notable in the West for fights involving ironclads, particularly the Battle of Angamos, which saw the only time ironclads were pitted against each other between the Battle of Lissa and the Battle of the Yalu River. The war helped formulate Captain Mahan's thoughts in