Is there any difference between "the causes of war" and "the causes of the war"?
Unless you mean the generalisation of a phrase like "the war caused the death of millions, the destruction of cities etc."?
I'm not sure if that works in English. I would say "the consequences of the war = οι συνέπειες του πολέμου". But then again english is my 2nd language so can't say for sure.
Casus belli is an act or event that provokes or is used to justify war. The causes are the actual reasons behind the war. For example the causes of a war are almost always economical ie. take another nation's resources to enforce yours, but the casus belli can be something like the assassination of Archduke Franz Ferdinand of Austria that provoked WW1, for example. Casus belli is a "proschema", a stated reason and not the real ones.