I have a suggestion which in my opinion will push players towards a conflucts. This is a CITY STORES. What i mean? Any other places has sort of limited store capsity. Like you full filled all your chests, all station all bank and thats it. You cannot simply collect your goods and materials. Instead you can convert your goods and res into money by selling it to city or simply by investing into city. You need it to upkeet the city BUT....you dont have to do it sort of like on daly basis. You simply can pay upfront. like one week/month upfront if you are very rich. so if everybody will do it then city can upgrade and live happily 1 year long. BUT all those res can by captured by enemy army and taken away from your store in case of sucsesful seige for your enemy.
So this i overlooked from Clash And Clans. But the only diffrence that in owr game players has alternative of diplomacy befor starting a war. But if someone grow to much in economy and start to be rude to neighbours then it can pay.