Laserburn

A skirmish level tactics game, written in 1980 by Bryan Ansell. This is apparently the origin of Warhammer 40,000.

Designed to be played with 15mm scale minis, the setting featured an Imperium that was sliding from techno-utopia to barbarism. It even featured the Inquisition.

It is, hilariously, still in print, as least in the sense that some website will sell you the books and the minis.

https://www.alternative-armies.com/products/lbr01-laserburn-rulebook