What did it cost Sauron to put his massive armies in the field? Presumably the orcs were slaves of a sort, being created beings, but he had a whole host of other forces who, at most, would have owed him some sort of feudal levy. And even his armies of slave-orcs would have cost him the expense of their equipment and sustenance.
Such questions are seldom raised in fantasy literature, especially when it comes to Dark Lords and Witch Queens, whose towering edifices and vast collections of servitors. This may be because the Dismal Science is usually either boring or terrifying, depending upon the extent to which the currency is collapsing, the markets are crashing, or the Gross Domestic Product is contracting.
However, an attentive survey of history will show that most of the exciting events around which fantasy literature is usually constructed – the rise and fall of empires, the bloody battlefields, and the crowning of kings formerly employed as discontented farm lads or Assistant Pig-Keepers – are often intimately connected with economics in one way or another. The conquest of India was less driven by grandiose ambition than the pedestrian desires of the East India Tea Company and its shareholders. The blind greed involved in forcing a conquered Germany to pay war reparations in a global economic contraction led to the bitterness that brought an Austrian corporal to power.
As Tolstoy noted in his own epic novel, the great waves of history that cause one nation to rise in terms of wealth and power also lay the groundwork for events of the sort that so absorb our literary efforts. Paying closer attention to these waves, to these primordial forces, strike me as a potentially fruitful vein for mining the conflict required to drive good fantasy fiction.