WW1 was inevitable. Blaming Gavrilo Princip is foolish, in my opinion. The assasination of Franz Ferdinand at Sarjevo was the trigger that allowed the war to spark.

The Schlieffen Plan was pure genius, and definitely intended for use. The naval race and colonial rivalry between Britain and Germany made matters worse. The Triple Alliance and Triple Entente meant that everyone would be pulled in when a war did start.

The Sarajevo assasination was just the trigger, if that had failed or not happened at all, there would have just been another trigger.