Nobody was prepared for them. For the portals to open. For the invasion.
At least, not in this way. They'd all seen the movies with the aliens or the illuminati taking over the world, with Godzilla, with Cthulhu. They were certainly not expecting bearded half-men with picks, axes and magma throwers.
The portals opened in many parts of the world, important and remote likewise. It wasn't even an organised invasion of any sorts, and the first mentions of these creatures led people to hysterics... of laughter. A man reporting savages with picks started digging through his basement, presumably to the other part of the world. A whole city claiming that their destroyed building weren't the result of some freak hurricane, but of some "reshaping" they could barely understand. Mountains defaced, at first attributed to alien messages and wonders from the sky. But it's not the sky they came from, nor where they were going.
And then they hit the cities. A concentrated wave of 50-60 for many a million-plus location. You'd think creatures like these would be easily killed by a sharp shooter or a missile. You'd be wrong. They brought their physics with them from their world. They brought what some said was magic.
They would raise walls around themselves, impregnable walls, unminable, untouched by radiation. Radiation, actually, it seems they were immune to, as they would be sometimes seen using pitchblende in the most uncommon situations, from making hammers to kitchens to walls. But the walls were the biggest problem: from granite, to obsidian, to soap, they were impregnable. "Roofs" had the same properties. You could nuke an entire city, and they'd still be there, long after the roaches would keel and die. More impressively (and especially worryingly) they were able to give the same properties to the outer areas of the walls they'd carve themselves, be it in concrete, soil or deeper levels. And the medieval "fortifications", that they would carve out of walls, would keep almost any bullet, any projectile outside, and make even sharpshooters for some reason flinchy and unstable.
And God did they smell. And drink. The first thing they'd do would be to raid liquor store, sometimes drinking on the spot, or filling their barrels on the same spot! They even had ways, those that retrieved some of the barrels would say, of putting "layers" of drink one over the other in ways that would not mix, but be able to be drunk each separately. They'd come out of nowhere, taking erratic paths, ironically quite the opposite of drunkenly, mechanical even, and take things, and store them for who knows what purposes.
The abilities they brought from wherever they came from were as marvelous as they were absurd beyond measure. Man always dreamed of breaking the laws of physics for their own purposes, dreamed of some better sorts of physics, but definitely not this. Great towers were raised, mountains were leveled, or turned into lakes, seas and oceans were bridged over... in stone, and some even reported levels of seas or oceans completely drained, while the rest of the body of water was standing at its normal size, but not advancing on their "fortresses", as if scared by the ferocity of their picks and their ingenuity.
Oh but they made beautiful things too. Incredible things. Men and women's eyes would water when they would see these masterpieces, guarded fearlessly by the dwarves, and for some it would be the last thing they'd see, and yet others would say that to have seen this, they must surely have died satisfied of life. There were some creations that would bend reality itself with their majesty, to the apparent lack of interest of their wearers. These were indestructible, and varied in form and utility. Indeed, rock glowing beds without coverings except exquisite jewels carried as shields and ponderously dragged everywhere were perplexing for anyone who watched such a weird spectacle.
They would eat just about anything except insects, bugs and the occasional small rat. Cats and dogs, beautiful pure-breed pets were torn from the humans and taken to blooded and bone-swarmed "workshops", they they'd be butchered, very often with axes. The only good thing was that they weren't cannibals, nor intending on using the remains of what was later discovered to be as "sentient beings". Though some groups would stoop as low as to hunt down and butcher humans to consume them and make bolts or spears or amulets out of their bones, these were fortunately the exception and not the rule.
But it wasn't an invasion in the usual sense of the word, as they didn't take lands, or keep them for very long, or used human industry to adapt to their own. Indeed, if only they had come along, maybe an uneasy truce might have been held between the two races. Since their arrival, humans had learned some of their language (for they didn't bother to learn the humans') and - after getting over the shock that it bore striking resemblance to many an ancient language of humanity - and were making headway with at least some of the tried. Uneasy peace was settled, merchants would come and go from their camp usually unmolested, and they didn't ask for much except raw and unique material - of which any human willing to trade was much in lack of, still they tried - and seemed to respect the truce upheld by the sanctity of traders.
But they did not come alone...
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OOC: I have some more ideas, but I don't know when or in what form I'll post them. Too much and too disorganized for now, but I'll see what I can do. Tell me if you like it/if you've thought about it/if it's been done before.