Essentially a Graveyard Crawl was a three-phased scouting and attack on a planet:
- First phase was scouting the planet and sending back the find, the scouts also secretly infiltrated the planet and teached Necromancy and magic in general to the natives, then went away to scout other planets. Planets attacked are planet-bound societies on planets with large demographic presence, it would change from planet to planet, but for our Earth, Earth from 1980 beyond would be ideal (demographic potential mostly taped), whereas the 2020 Earth from that universe I made was already bordering between "ideal target" and "too advanced" (because most nations had a space fleet, some quite big, if antiquated by Dead Nations' standards).
- Second phase was the proper attack: Essentially, a magic spaceship arrives, they use their magic to find out all the interesting magic users on that world and indulce them through mental magic to enter magic portals to the spaceship. After that, they bombard the planet with a few small-sized meteors painted with enchanted, radiated runes that make all dead rise after death, and hit the main locations that would weaken the planet, then go back to the main planets turn these wizards into proper imperial ones while the planet has a war between living and dead.
- Third phase is when the a Tomb-Ship arrives to the planet, collects the dead (assuming they won the war) and goes away so they can grown and get reaped again. Sometimes the planet is deemed suitable for colonization, in this case a large colony ship comes escorted by some war vessels. In case of colonization, the dead remain to work on colonization, armies are sent to place the natives as vassals/reservation, otherwise the tomb ship leaves with zombies.