First would be to analyse the "powder keg" theory to the outbreak of World War One, to see which countries were involved in the outbreak of World War One. In 1907 you already had a major split between great powers in Europe, The Triple Alliance 1904 (Germany, Italy and Austria-Hungary) and The Triple Entente 1907 (Britain, France and Russia). This was a evident factor as to who fights who an for what reasons. The two alliances, aware of rising tensions, began their preparations for war long before 1914. The Naval Race began between Britain and Germany. Germany had their Risk Theory, to create a big enough fleet to threaten Britain's fleet to stay in their ports. And Britain had their "two power standard", for their fleet to be big enough to fight two major naval powers at once. This reasoned to long-term tension before the war.
The Great Powers also began their preparations for war on land long before the war broke out. Again, Germany created the Schlieffen Plan 1905. Named after German general Count Alfred von Schlieffen who created the plan, which later proved unsuccessful (arguably, they didn't actually follow the plan). The main idea of this plan was to avoid fighting a war on two fronts simultaneously, first take out France in the west and then move to the East and fight a slower mobilizing Russia to the East. Now it is true to say that expansionist Germany had the most aggressive and ambitious offensive plan of all the European countries. But could then mainly be accused