There are five ages in Empires, and each one has its own military and economic strategies needed to fight and live through it successfully.
(950-1300) The medieval age is the first of the game and has the least advanced weapons, but not necessarily the least complicated ones. In several ages of the game, combat features a triangular relationship not unlike the children's game rock, paper, and scissors. In the medieval age, all swordsman are good against archers, all archers are good against spearman, and all spearman are good against swordsman. Every civilization has all three of these types of units available; however, whether they are in infantry or cavalry form varies. Siege weapons also exist and can be countered by several different types of land units; they are good against buildings and moderately effective against ships. Towers and walls in this age resemble castle walls, and fire arrows. Ships and their strengths vary from civilization to civilization.
(1300-1600) The gunpowder age is the next age after the medieval, and is arguably the most transitional age in the game. Early riflemen are now thrown into the mix, and with the new units mixed with the old ones, there is a very complicated unit system. Siege weapons become more refined, and units that will be predominant in later ages start to appear. This is the first time units can be updated, and many units are added for every civilization. However, at this point, no units have been removed. Also, all walls and towers have been updated to shoot cannons, as have all battleships.
(1600-1900) The imperial age is the final age of the first four civilizations, of antiquated buildings, and many types of units, such as cavalry and religious figures. The triangle in this is swordsman are good against rifleman, rifleman are good against siege weapons, and siege weapons are good against swordsman. This age has what looks like the common cannon, and soldiers have the general look of the Napoleonic Era. Walls and towers remain the same, but battleships once again receive an update. The imperial age is also a natural time to have as a last age in a battle, considering how many concepts change between the imperial age and World War I.
World War I
(1900-1935) Although the real World War I only took place during four years in the late 1910's, in the game the World War I age spans 35 years. The onset of World War I is the most dramatic change between any two ages, with all units updated and older civilizations replaced by their modern equivalents. Towers and walls appear more modern, and infantry and siege weapons are completely transformed. Many units such as cavalry, temples, and traditional infantry and warships suddenly become obsolete, and the introduction of tanks and aircraft changes the strategy of the game. World War I is also a natural place to begin a game.
World War II
(1935-1950) World War II is the last and final age for Empires: DotMW. World War II upgrades some existing units from the previous age, as well as adding some, depending on the civilization. World War II also is the only age where wonders can be built. Wonders add a slightly new angle to the game, and can only be built with a huge amount of resources. The triangle in World War II is infantry can defeat anti-tank weapons, anti-tanks can defeat tanks, and tanks can defeat infantry.