The military in SimCity will usually ask the player for permission to place a military building in their city, which generates money at the cost of land and desirability.
In SimCity 2000, when the city is big enough. the government will ask the player to allow a part of the city to be in military use, such as an airfield, but it is placed randomly in the area.
In SimCity 4, you can simply unlock a military base, which is a business deal awarded after running low on the city's funds, but also take a lot of place, like in other games. The player cannot invade or attack other cities using military, although some disasters are similar to an attack, although not a ground invasion.