So previously, the system was pretty much just "execute a command and the person who kills the king becomes the new king". In concept, this is pretty good but, due to several issues with the system, it had to be removed not too long ago. The purpose of this suggestion is to offer a possible solution.

Here are the steps for this new system:
1. Politics: There needs to be a reason to overthrow a current system. Whether you employ spies to gather and spread rumors or take a more public approach is completely up to you and your political strategy. Regardless, it is within your best interest to gather the support of several mayors at some point before or during the Coup process. This will come in handy during the succession phase
2. execute the /coup and /coup confirm commands.
3. every single mayor in the nation (even if your town is occupied by the nation) will receive a message when they log on stating "Someone has started a coup! What will you do?". From here, the mayors have two buttons to press: A. Defend the current King or B. Support the Coup (it's not actual buttons. Type either A or B in the chat and press enter. This way, minechat users can still vote). If at least 30% of the mayors agree to a Coup, the coup will begin. Keep in mind that all of this is anonymous. Because occupied towns can vote, it is very important that Kings do everything in their power to either keep their occupied mayors happy or remove them from power
4. The person who initiated the coup command can end the coup by either killing the king or being killed by the king. If they are killed, well good luck to them lol. If they kill the king, the nation will enter the succession phase. It is at this point that everyone in the nation will receive a message upon logging in that states the name of the person who initiated the coup and who won the battle. This battle lasts a maximum of 7 days. If the King doesn't log in within these 7 days, then it will count as a loss on their part. Same thing for the person who started the coup. If neither log in during these 7 days, the coup will be canceled and the name of the coup starter will not be revealed as if the command was never executed.
5. Succession phase: Anybody (even citizens) can execute the "/succession claim" command. What this does is that it solidifies you as the leader of a Party who now has a claim to the throne. Each Party leader can "/succession invite" towns of the nation to join their Party. Like I said before, this is why Step 1 is so important. If you, as a Party leader, do not have even one town (that isn't your own) to support you, your claim to the throne will be removed (your party will be deleted). Partys can also merge using the "/succession pledge " command. What this does is that the person who executed the command gives up their claim to the throne to the Party leader that they wrote and all the towns that they previously collected will join the other person's party. The gathering of the Partys lasts 48 hours and starts the moment the previous King loses.
6. After the mentioned 48 hours have passed, each Party will participate in a siege on the capital of the nation. Once started, the siege will work just like any other siege. Of course, since the siege is taking place in the capital, the previous king will have the advantage of home turf and whatever cannons they might have already built. If previous king is smart, they will have started a Party themselves. Whichever Party leader wins the siege will become the new King. After a new king is made, no coup can take place within this nation for a month.

Note:
Ok, what happens if the nation gets attacked by an outsider during the Coup phase and/or Succession phase? Well, members of the nation can still participate in international sieges to defend their nation. Will they work together? Well, that's up to them.