Fields of Blood is an add on for fantasy d20 that describes a system for realm management and mass battles. Overall, the realm system is comprehensive and workable, if clunky. With provinces generating different amounts of resources based on improvements, tax rates, government styles, and random events, it immediately has me reaching for a spreadsheet. I'm not sure that there's a way to do this sort of thing elegantly, particularly in the d20 system, but expect to do a lot of calculation to watch your realm grown.

The second part of the rules are a mass battle system. Regular d20 stats are translated into Field of Battle stats through yet more formulas (the phrase "divide by five and round down" appears several times), soldiers are group in companies of 100 men, generals are assigned, and battle takes place in a kind of Warhammer-like framework. This is where I start to get have doubts about balance. Dealing damage is a two-stage attack roll, first to hit and then to toughness, and most units can take take two hits. The game gives example default stats for a regular medium infantry unit, your basic trained soldiery, who hit each other on a 14 and deal damage on an 11. This means that any attack between identical example infantry has a 16.5% to go through, which means that standard infantry combat is slow, maybe 10 rounds of attacks. Worse, the example heavy cavalry unit, which costs twice as much the medium infantry, is effectively invulnerable to the medium infantry with about a 1% chance to get hurt. And these are the examples printed in the book! I need to look at the system in more depth, but I'm fairly sure that it can be broken like dry spaghetti.

The last third of the book has lots of familiar D&D spells and monsters translated to work with Fields of Blood, but I would've have really liked to see more examples of troops that might actually show up, as opposed to stats for armies of Achaierai, Driders, every type of Giant, Golem, and Elemental, and outsiders from Astral Devas to Vrocks.

I have some design disagreements as well. This book doesn't handle magic items gracefully. That standard medium infantry unit costs as much per season in upkeep as a Wand of Fireballs. I don't think I need to say what the equivalent of a modern grenade launcher would do to a shield wall. For all the focus on magic and management, there's little about how communication spells and Decanters of Endless Water would change warfare. The system for assigning heroes to lead units is clunky, even by the standards of Field of Blood. And the math errors may make the battle system completely unbalanced.