To put it simply you need Villains. Also known as Antags. To some, also known as Griefers (though that isn’t exactly what they are).
More common on servers with Roleplay as a focus in varying degrees, but it can apply to non-RP as well. You need a certain subset of the population to simply play the part of ‘bad guys’. These are ones who’s sole purpose is to incite conflict between players.
Unfortunately this isn’t very easy to pull off. Believe it or not, most people do not simply like to engage in conflict with someone unprovoked. This applies mainly to Real Life, but also in video games as well. So in this sense most players need some sort of Casus Belli (Cause of War) to engage in conflict. But your villains or antags need to be able to do this without any provocation. They need to be able to stifle the natural urge to avoid unprovoked conflict.
When you’re around friends its a little easier. When you’re with people you’re used to being around, you naturally test boundaries in a friendly atmosphere. But going to a random strangers sandstone hut and blowing it up. Well its a bit tougher. Which is why so much drama happens, even on PVP servers, when someone gets the nerve to actually do it.
But if you want PVP, then someone has to do it.
That someone will be a target. That someone will be the focus of ire. That someone will be the recipient of every bad omen imagined or real that happens from then onward. Which is why in many cases, normal people hate picking up that mantle.
When a player does pick it up and does so knowing that it is good for the players and the server they play on, do so with restraint, and don’t take things personally. Then you have a great thing. But as a server admin you will need to ensure that such a player isn’t mistreated in turn. Like I said, they will become the ‘bad guy’ and will likely get blamed for problems they didn’t cause down the road.
On the other hand. If you get a bad player in that role who relishes in the misery they cause. Then you have a really bad problem that can infect and destroy a server. You have to make sure these players don’t fill these roles and make sure people in the above paragraph don’t fall into this when things invariably start getting ugly towards them.
You could do it yourself, but unless your general population is mature (randoms on the internet are not) enough. You’ll likely end up with accusations of admin abuse and other shenanigans. So usually you want players to step up to the role whenever possible. Doesn’t mean you can’t, just I recommend admins not being the sole villains on the server.
The only exception to that is if you are playing on secondary accounts as sort of NPCs. But this is very much akin to PVE with a GM playing the NPCs. Not exactly a PVP atmosphere. But it can be useful to get players used to fighting foes that aren’t simply computer controlled mobs.
Give thought to maybe contacting some of the more mature and helpful players and see if they’ll provoke some attacks here and there. When players see other players fighting, they start seeing it as more normal and will likely follow suit. The best way to start PVP is to PVP after all.