Long time ago, I played with a 4x game looking like a kind of Gal Civ ancestor. Unfortunately, I can't recall its name.

In this game, in order to invade and conquer a planet, you had to build ground forces (tanks & troops) and load them into transport ships.

Invading the planet and fight down there was the only way to conquer. Of course, tanks & troops had to be be trained. It was also possible to upgrade them such as battle ships in Gal Civ. They were gaining experience as well.

The gameplay was significantly enhanced as it was not only a math calculation for winning a planet like Gal Civ.

If the player was smart enough to defend its planet, using ground particularities for instance, it was possible to defeat an invader more numerous or slightly better equiped.

I'd like very much to see this implemented in Gal Civ III.