Was alliance the most important cause of world war 1?

Basically. Austrio-Hungary wanted to invade Serbia, so Austrio-Hungary sided with Germany. Serbia called upon Russia, who called upon England. the Ottoman Empire sided with Germany, and when Germany invaded France, France sided with England. Romainia kind of went with Russia and Bulgaria went with Germany. Italy sided with England to invade Bulgaria. Add all of that together, plus the fact that the African territories of the European Nations declared war on each other, and Japan wanted territory, so it sided with England. Japan invaded China, so China sided with Germany. The Arabian nations wanted territory from the Ottoman Empire, so it sided with England. Eventually the United States entered the war on the side of England. Add all of that together, and that is a World War.

So as a basic recall, England, France, Italy, Serbia, Russia, The Arabs, Japan, the Allies' African Territories, Romainia, and the United States were on the Allies, and Germany, Austrio-Hungary, The Ottoman Empire, China, the Axis Power's African Territories, and Bulgaria sided with the Axis Powers.

There may be some other countries partially involved that I haven't read about yet.