seems i get razed in the mid game cause i don't focus enough on military units. wonder how most players balance this..(like right when combustion comes in)

i play Roosevelt on warlord

You should have at least 1 or 2 military production cities that basically just build units the whole way through (except if they need a building to grow health/happy caps).

There are several ways; check out some of the ALC games for examples... (links in my sig) :D

In general, fighting a war earlier in the game will usually leave you with a large standing army of veterans (with advanced promotions) that you can upgrade.

Along with that or alternatively, just alternate your builds. After every "civilian" build, do a military build that adds to your power rating and/or military capabilities (units, barracks, stables, drydocks...)