The idea was that there's a time limited map (usually 2 months) and players team up as a faction. A faction could own land, paid through in-game money earned by mining ores. Blocks inside your land couldn't be modified by non-factions players, but you could give special permissions if needed. The hardcore part was that every death of any member of your faction would decrease some power value and once that crossed below zero, your land protection was gone and your base was usually grieved instantly. So there was always a thrill of going outside. There were a bunch of server wide events that encouraged going outside and gave you in-game rewards.
What made this server special was the permissions mentioned before in combination of everything minecraft, and especially redstone, made possible. We build all kinds of special contraptions live banking vaults, slot machines, trading machines and a lot more. That was in stark contrast of most other factions that focused mostly on PvP. In later maps be earned enough reputation and were usually not touched by major PvP factions. The combination of hostile environment and the ability to be really creative thanks to minecraft was great. In case anyone read all that, here's the bases we build: https://hcfluffy.de/bases/