ETA: Never mind. Found it myself. It was the Settlers II.
* Background: I played in college on my computer. Unfortunately I can't remember many details about the game, it just popped into my head the other day, and I'm trying to track it down.
* System: Mac OS (7? Definitely classic)
* Year: Available as a cracked version on a college network 1998-2001. Don't know the original date.
* Perspective: 2.5d
* Art style: Sprite, I think, definitely cartoonish.
* Environment: Wild lands, forested, mining, quarries, etc.
* Mood: Cheerful, optimistic.
* Genre: About 70% certain on RTS, otherwise turn based.
* Gameplay: Resource managment, resource production. I don't remember controlling units the same way as Warcraft, I think it was just a limited number of units and buildings produced resources directly, but my memory is extremely foggy. You were controlling a (Pseudo) Roman colonist group (after a shipwreck, I think), building up their colony to achieve certain goals. I don't remember the challenges in detail, but at some point you encounter another group that was definitely a shipwreck, Japanese (Using Nippon or a variant spelling in game). I'm pretty certain that the group wasn't actually identified as Roman (it wasn't Caesar or any of those), but the imagery and themes were pretty definite.
Sorry for the lack of details.