I guess it all depends on how big you want you map to be. :)
Battletech and Alpha Strike both focus on relatively small patches of land, maybe a few kilometers across at the most.
Battleforce scales this up, to the point that a few mapsheets can represent an area tens of kilometers across, such as a major city.
Strategic Battleforce scales this up even further and can be used for battles assumed at controlling an entire region.
Abstract Combat System is the next one up, with maps representing entire continents, and a few scenarios able to decide the fate of a world.
Inner Sphere at War is the biggest system, and plays out wars at an interstellar scale.
All of the systems from Battleforce on up can be found in the same book, Interstellar Operations: Battleforce.