Age of War is a quick-playing game of conquest. Fourteen cards are laid out at the start of the game, each showing one castle and the symbols required to conquer this castle, with the symbols separated into battle lines. Each castle belongs to a clan, with some clans having only a single castle and some having up to four castles.

A player starts his turn by rolling seven dice, the six sides of which show archery, cavalry, daimyo, and 1-3 infantry. He then selects a card and uses the symbols rolled to conquer exactly one of the battle lines on this card (by placing the appropriate dice on that line). If he can do this, he then rolls the remaining dice, ideally conquering another line; if he can't conquer a line, he removes one die from play, then rolls again. His turn ends when either he conquers every line on the card (in which case he claims it) or he no longer has dice available to roll.

Each card is worth a number of victory points. You can conquer cards owned by other players, but you need to conquer an additional daimyo line in the process. If a player owns all the castles of one clan, however, those castles are secure and cannot be stolen. What's more, these castles are now worth more points because you've united the clan under one ruler (you) and strengthened your hold over Japan.

When the last card is claimed, players tally their points, and whoever has the highest score wins.