I found a medieval themed modded server for Java 1.12.2 where the main idea is building kingdoms and fighting wars.
The big mod focus lets players make NPC soldiers and workers and you can also use siege machines like catapults to attack fortresses. Wars are long term and sometimes lead to big battles with lots of NPCs and a final fight at an enemy capitol.
There is claim protection most of the time but it gets disabled during a siege for wars. The server has some lore and rp going on with a backstory posted in their community but roleplay is not required.
It is not only war since there are building mods and lots of PvE too. You can find structures and bosses and they also plan PvE events sometimes. Notable mods mentioned include Ancient Warfare Mowzies Mobs Electroblobs Wizardry Epic Knights Quark Waystones Biomes O Plenty Rustic and Travelers Backpack.
