I think it would be best if the motive for war would be mainly (economical)..for example
you have a mining/oil corporation and an other country has the same and his corporation is growing faster than yours..or his products are monopolizing the market..then it would be a good Idea to ignite war with that country after long diplomatic communication to come to an agreement so both parties are satisfied..
as mentioned above,simply you have a gold corporation (You sell oil)and its your most successful business you are running and then an other country flourishes in that business and starts to sell his gold in a lower price..so others will buy his goods rather than yours..
the game has a messaging system..you simply message him"OK your price is too low and and I'm incurring economical damage..would you please raise you price?"..he says yes and things will remain peacefull ..he declines and you start to think of and prepare for a large scale military campaign..this is the way it must be and this is the way it is in real life.