I'd look at the demos.
Lock 'n' Load is a non-computer board game, but a neat one. Similar in genre to Squad Leader, but nowhere near as complex as Advanced Squad Leader.
I have rather enjoyed playing The War Engine, and would recommend trying the demo. Could be close to what you are looking for, though PBEM rather than "online multiplayer".
The Combat Command games are also a neat WW2 system that isn't too complex (I guess it's more wargame-ly than The War Engine, though, so it might seem more complex if you're not used to wargames - again, try the demo), especially if you're not an armor grognard. Again, PBEM rather than "online multiplayer".
M.U.L.E. is a classic game from the original Electronic Arts (back when it was a small and very creative game development company) for the Atari 800 back in the mid-1980's, which was about economics on a frontier space colony. Space Horse is a tribute to and extension of that concept and style.
You might also peruse the demos of:
Empire Deluxe Enhanced Edition
Slay (
http://www.windowsgames.co.uk/slay.html)
People's Tactics (free)
PvK