Considering the european nations already had defined alliances, do you think that war would have been inevitable? must be in three to five sentence : /

Well, I think that in principle, every war is inevitable until it happens - perhaps, if the fall of the Iron Curtain had resulted in war we'd be calling it "inevitable" now. The war was however very predictable at the time, indeed due to the alliances. In fact, Otto von Bismark had long before seen the potential for war in Europe, due to the national conflicts and strong alliances, as seen in his quote: "One day great war will come out of some  foolish thing in the Balkans"