There were only two sides - "The Arm" and "The Core" - cloned humans and robots respectively with essentially similar units, although Core units tended to be tougher and slower. The game made up for this by having a LOT of units (Air, Naval, Ground, Amphibious, Commanders that nuked themselves when they died) and buildings (particularly a massive number of fixed gun emplacement types), (effectively) endless resources (Metal and Energy), and comprehensive control options.
This game was best experienced with the expansion "The Core Contingency" - or "C.C" (eg: Submersible Aircraft, Anti Radar and Anti Sonar units, more Submarines, AA Ships...) together with still more official downloadable Cavedog units (eg: FARK's, Mobile Anti-Nuclear Missile Units). Has it been mentioned that this game had a LOT of units?
Cavedog used to run "Boneyards" (similar to Blizzard's "Battlenet") which was the optimal place to enjoy T.A in multiplayer. Players could elect to play for either side in a constantly refreshed galaxy of planets - where the results of one's games would decide whether the Arm or Core dominated at any given time. Boneyards also had an military style ranking system based on a player's wins.
In closing, T.A was a remarkable game for its time and for sheer strategic and tactical options it would compare favourably with any RTS currently on the market.
T.A has a LOT of units.
NB: There is an "unofficial sequel" to this game being developed by Chris Taylor (now at Gas Powered Games)called "Supreme Commander".
T.A noob: "Can I join your game?"
T.A veteran: "CC?"
T.A noob: "...What is CC?"
T.A veteran: "FARK off."
T.A noob: "Why no Flash Tanks?"
T.A veteran: "No EMP's!"
T.A noob: "You just can't handle a rush!"