Empire Earth is a real-time strategy game developed by Stainless Steel Studios and published by Sierra. The lead designer Rick Goodman is best known from Age of Empires and you can definately see the resemblance between the two games. The main thing that sets Empire Earth apart from other RTS games is the massive time span it covers. The game lets you do battle with units ranging from prehistoric cavemen to futuristic mechs.

You can play various (semi-)historical campaigns, user-made scenarios (the game includes a very sophisticated scenario/campaign/map editor) and random map games against the AI and human opponents.

The gameplay will be instantly familiar to anyone who's ever played Age of Empires or some other RTS game. You start with a town hall that can create citizens which are used to harvest resources and build other structures. There are four resources in Empire Earth: wood, stone, iron and gold. The epochs (similar to the ages in Age of Empires) range from "prehistoric" to "nano-age" and each has its own units or improvements.

The total number of units is somewhere beyond 200, including ground, sea and air (in the later epochs) forces. As you advance, you can upgrade your infantry units' swords to gunpowder weapons and siege weapons to artillery. You can also choose to improve any one type of unit with better damage, range, speed, hitpoints or armor. In addition to conventional units, Empire Earth also has priests and profets that can convert enemy units and call calamities upon them.

Official site: http://empireearth.sierra.com/