that is WWI stuff :^)
maybe something like this (this is from an American POV)
Land:
Modern Era (first world nations would begin with about lvl 8 already, everyone else would be somewhere lower) - sprite should look like 80s US soldier or modern third world, second world
Future War (began with introduction of Land Warrior system in the US - '93?) - modern us soldier, some other nations as well
War Without Man (around 2022 or whenever you all think humans will play less a role in combat, ie introduction of remote piloted tanks, more planes) - the Future Warrior battle system...black body suit, looks scary
Artificial War (when human infantry are replaced with robots/remote piloted - i figure around 2100) - something similar to the freaky mech warrior looking thing some defense contractor came up with for the gulf war but never made (far as i know). it's like 8 feet tall, covered with spectra and armed with a .50 cal machine gun in one hand
EDIT: just looked up the end date of 2200 (little far, eh?) anyway, i changed some dates.
-Matt