[PTTG]

All of the above. Mars' hostile climate means that even well-prepared military bases can and have been destroyed with all hands by avalanches, storms, lava flows, and the other hazards of this larger mars. This means that military conflicts here have plausible deniability to prevent the cold war from going hot just because the soviet martians raided an Allied mars base or vise versa.

The question, of course, is what the bases are there to find. And that's where MDL v3.2's point comes to the fore; Mars has life. What form it takes is hard to say, but it is clearly so deadly that its previous attacks have left no witnesses at all.