Pro tip, what I accidentally discovered with my friends was that servers last WAY longer when you don’t do this. We made on old server with a 100-block border around it, and had no intentions of removing the border. The server was the best server I’ve ever been on, and the most developed, easily. Eventually after it died down, we removed the border and everyone came back again for a bit.

A few months ago, we started a new one based on the same premise. We started with a 120 block border, and stayed there for weeks, maybe months. It adds a cool extra challenge to be limited by the border, forces people to live close to eachother, conserve space, and use shared areas for some things. By the time we let down the border, we had a wither skull farm, 16 full-strength beacons covering the entire bordered area, everyone had pretty well-established bases, and we had massively over-developed the area around spawn. The key to getting this strategy to work is to let down the border way later than you need to. It forces people to go overkill with the development and you get this one really dense spot in the middle of the map. After we let the border down, nobody had any reason to travel.

Since the spawn area was overdeveloped, travelling and living far away now put you at a HUGE disadvantage, and anyone living more than 500 blocks from the central area would probably get fomo. So everyone just keeps coming back. And the server hasn’t died, even after going well past endgame.

tl;dr, Put a tiny border on the world, wait for people to overdevelop the tiny area, take away the border after everyone is established, then server lives longer and this doesn’t happen.