>>719105409 (OP)
Try Imperium Galactica 2: Alliances. An absolute gem from Hungary, 1999. A hybrid grand strategy / real time strategy game set in space and planets. It looks surprisingly good for a game from 99, full 3d graphics and all and it has a miryad of mechanics that are easy to learn but hard to master.
>terraforming, colonization, colony building on planets
>ground combat on planets
>fleet combat in space in which planetary defenses and orbiting space stations can take part if they are nearby
>espionage, sabotage, terrorism
>trade of military surplus via markets
>research with various branches
>a very extensive diplomacy system that allows you to do negotiate about pretty much anything
>you can design your own tanks and ship classes using modules you research or even steal via espionage from other races
There are also 3 campaigns for the 3 major races, which consist of a major plotline and numerous randomly generated encounters and sidequests for great replayability. The campaigns also have exclusive mechanics in them, such as pandemics, mafia takeovers of planets, threats of apocalyptic meteor storms, and more.
Besides the major campaigns, there are also dozens of simpler scenarios with just one major objective, and their own settings and quirks, and of course, a skirmish mode.