The problem your having is your controlling the element of gameplay to much.
War, unfortunatly is something that players love to do. The reason being is competition. Mind you not everyone wants to do it, but there is 0 competition in your game right now. You need some element that keeps everything at bay, keeps you holding onto the game, keeps you coming back for more. Right now as it seems, what you do in the game is...well nothing. There is no penalty for not doing anything and no penalty for just doing things. The progressional chain that you have reeps no rewards towards a show off system.
You could add some way to make it so you earn items, collectibles etc that give an advantage. Or hold a social aspect of voting for best town, house, farm something. What you need is a socially driven magnet on making someone better than the joneses. Or add in PVP and allow people to kill eachother off. That will form alliances, guilds. Maybe accelerate your time a little, you said you wanted it close to historically accurate right? Why not have contributions towards a war that happened, have people make blackmsiths, do missions making weapons etc. You can have alliances that attempt to make more resources for the war.