If you can have a giant walking robot as armored as a tank, I don't see why you can't have a giant walking bug as armored as a tank.
It was recently reported that DNA has been used to self assemble carbon semiconductors; as far as I'm concerned, someday I'll live in an orbital tree, and fly around in a space whale, both of which have grown nanotube and graphene skin and bones, while my ass stores self grown carbon computers to augment my brain. No more sitting at the computer, I can now sit on it. [fonzy]Eeeeh.[/fonzy]
It would actually be a bit more interesting for only humans to have tanks, given that the first World War was a rather unique situation. It wouldn't be out of the question for no one else to have had the pressure to develop extremely heavily armored, mobile direct fire artillery, to traverse otherwise impenetrable defenses, and overcome lack of communications by brute force. Everyone else could have very heavy wheeled, or legged, vehicles, or creatures; those would by necessity have a lower maximum tonnage with high or lower speed. However, tracks are pretty simple, and even if you just see them without touching them, I wouldn't be surprised at the Tarka going, duh, and whipping out their own refined tank design in a year, vaguely like the Japanese with guns after the Dutch introduced them. For the Hivers, a giant armored snail (so damn silly) slower than anything else, but still fast enough, and with the highest possible tonnage.
Okay, that's too much, other than the obvious time sink it would be to make every faction unique to that degree. I don't seriously think any of this will be done, but I'm having fun, and I'm on a roll, so I'll keep the spiel going.
- Liir: just ever larger cetaceans with awesome mind powers, giving a very direct, bigger is better.
- Morrigi: everything either flies, jumps, or is air droppable, and is therefore very light, or they start with antigravity which I don't think would be as interesting, but which may be more correct. They would use lots of automated scout drones.
- Zuul: fairly conventional, but with baby swarms, and maybe a ground based node weapon would be fun. Maybe they're orbital support is a little sloppy? Maybe those babies would have cameras implanted in them to act as scouts?
- And the new guys, the Loa (I know they don't fit the time frame, right?): I want to say they just grey goo everything, cause you know they want to, or that they would have a unit analog of everything out there, but both sound wrong since they're so obvious. I think they would go really small, and widely swarming, ie swarm of explosive butterflies, precision orbital artillery instead of ground artillery, and fixed position, high range, relays as commanders with very high command/support range. Something like that, something which places them more in orbit, using absolute finesse, and standing off completely out of real danger. Maybe they get more and better cards for orbital support.