For Whom the Bell Tolls is the novel about the Spanish Civil War, and it describes the uniquely cruel reality of war violence in all its grisly details. In this novel, war seems to escalate beyond human control, thwarting the best-laid plans of any commander. It deprives individuals of their loved ones, forces them to kill their countryman, and spreads barbarism. Perhaps most troubling of all, war releases the darkest side of human beings: the lust for blood, the pleasure in slaughter, and the madness for revenge which make killing possible, even desirable, for many of those who fight.
Pablo initially relishes the war because it gives him free reign to satisfy his bloodlust.
There is no single person or authority with real control over the course of the war on either side. War, as we see it in For Whom the Bell Tolls, is the product of large number of individual actions and accidents, which can only be loosely managed by the people supposedly "in command."