As I am so far as I know the only guy who knows how to be a diplomat on this server I have decided to make a guide seeing how at some point the server will have a Global War and it is best that nations have allies to back them in case of a Napoleon leader coming up and taking over the towns world.
First step is when ever you are talking to a nation leader you always sound super nice and smart so they know that you know what you are doing. So they will actually listen to what you are purposing.
Next it is best that when asking for an alliance between your nation and theirs you promise to back theirs in a time of war so that way they know this isn't some joke. I highly recommend you be honest about this and tell your leader this
Finally make sure you jam their chat full of facts why they should say yes to this alliance and no facts must repeat its self or else they may loose interest and if that fails then just ask them why they wont say yes and change their mind by telling them that your nation doesn't do what ever they are assuming it does. (only do this if it is the truth.) If the fact they bring up is true then you might have to give up and move on.
Simple as that and under the circumstance that everyone makes alliances it would be best to do some research on your ally in case they are in fact a barbaric nation that will betray you if they see the opportunity.