They had discovered alien life before, of course. One did not expand across such an unknowably large distance and fail to find habitable worlds. But nothing like this. The hives covered the planet’s surface; swarming, seething masses of them. Even orbit, so serene above the surface of the homeworld, was choked with them. Further away, lights in the dark indicated ship drives, flitting around the edge of the system. They all felt a deepening sense of claustrophobia as the armada passed through the gate, a wretchedness verging on suffocation.

They had found the outer edge of the new species’ expansion years ago, an isolated ship riding a beam of subnuclear fire. Their armada had waited, not really knowing how to begin communicating with such an alien race. But they didn’t have to wait long; the explorer ship remained silent for a few days and then broadcast a perfectly formed reply in their own language. This ability was, needless to say, impossible. As they began to understand the content of the explorer’s messages, that promised kinds of sharing and mind-alteration strange and obscene, the aliens’ technological powers became more and more apparent.

The various messages were untangled. Each new idea was more strange and terrible than the last. These aliens lived within a dream, motivated by things that didn’t really exist, supporting their insanities with godlike powers. Conflict was inevitable. The foreign vessel extinguished itself before it could be captured. But all was not lost.

They assembled all known ships – every ship ever built, everything that could carry a weapon from every corner of known space. Old conflicts and rivalries were ignored, fading into irrelevance in the face of such a titanic struggle. Coordination was simple and immediate. It was not a matter of discussion or cooperation. Rather, it was simply the case that new information became available and everyone, everywhere came to the same conclusion simultaneously. They had the advantage, if they took this last, desperate step. Their way of life could survive.

The alien home system was dense with replicating machines, but they waited inertly and responded far too slowly. The route taken enabled a surprise attack close to the alien homeworld. They possessed few weapons in the instant of meeting, but the capacity to create them had not been forgotten. Surprise was necessary.

More messages were beamed by the aliens; demands for unity and understanding where none could exist, requests and pleas, digital pulses that seemed to want to bypass their minds entirely.

They ignored all these, for their course had been decided upon since they had received the first messages from the lone explorer that had crossed their path. The logic was clear to all who observed; they could risk servility, extinction or corruption or strike fast and deal with the aftermath later, for these two species could ultimately never coexist in the same universe.

They did not wish to exterminate, merely to contain, to quarantine, so that understanding could take place on their own terms. Maximal force was required. Projectiles were deployed, targeting centres of communication and the spindly webs strung in orbit; any resistance, any blizzard of kinetics or electronic warfare was dealt with by deorbiting a habitat. Asteroidal material was flung at the planet and its single large moon. Their command of the alien language was marshalled and used to broadcast an ultimatum to the rest of the system, showing that there would be no compromise, that opposition was to stand down or death would come to all.

The aliens understood.