I found a medieval themed modded server where the big idea is building kingdoms then fighting wars with sieges. The main mod lets you make npc soldiers and workers so you can have real armies and not just players.
The server runs on Java 1.12.2 and it started last week so people are still forming kingdoms. There is claim protection but it gets turned off during a siege for wars so battles can actually happen.
It leans into castles and towns with building and furniture mods plus extra blocks for stuff like bridges and windows. They are also pushing lore and rp more and there is a backstory on their Discord but you do not have to rp if you do not want to.
Wars are long term and sometimes there are big battles with lots of npcs plus siege machines and knight gear. The goal can be taking multiple bases then going for the enemy capitol in a final battle. If you want action without pvp there are pve structures bosses and they plan some pve events too.
