Defending a Kingdom is simple, and it starts with a good castle.
Like in medieval times, castles are the center of any Kingdom, and fortifications and defenses were the highest priority in hostile times. Medieval Unlimited is no different, and unless your Kingdom has a shield active, you can guarantee you will be under attack soon - especially if your Kingdom starts to retain wealth and expanded territory.
Unlike other servers, players are NOT encouraged or expected to "play fair". Objectively weak but wealthy Kingdoms are an easy target, and everyone is on the look-out for an advantage to climb the ranks. If you want to drastically increase your chances of survival, follow this guide on how to properly defend your Kingdom.
This server often draws in creative builders with unmatched skill in creating beautiful architecture, but that simply is not what Medieval Unlimited is about. If you want to survive any length of time, accept that building the most detailed castle you can imagine is not realistic for a new Kingdom. We HIGHLY recommend taking a 'defense first, detail second' approach. Start your build by building entirely out of stone like cobbled Dacite, and prioritize making defenses first like thick walls, battlements, loop holes, bastions, and more. Only after you are sure it is safe, begin the process of making it pretty.
Think about how players might try to breach your castle. Are your walls thick enough to withstand more than a single trebuchet hit? Can they be jumped over by creating a dirt tower or by a horse? Do you have the advantage of height and cover while defending? Do you have multiple layers of defenses if players do breach your walls? Is the chunk of land your Nexus is on totally within your walls?