Why were alliances a main cause of world war i?

alliances strengthened demands for self-determination.
nations were less likely to use diplomacy in settling disputes.
if one nation was attacked, the others would come to its aid.

The right answer is:

If one nation was attacked, the others would come to its aid.

The first two options are generical issues that cannot be proven historically.

On the other hand, the obligation to come in aid of an allied nation was a real factor in the origin of the war, that lasted from 28 of July, 1914, to 11 of November, 1918. The historical reason was the assassination of Archduke Franz Ferdinand, heir of the Austro-hungarian empire, by serbian nationalists.

Because of this incident, Austria-Hungary declared war on Serbia, and shelled its capital, Belgrade.

And after that network of interlocking alliances enlarged the crisis from a bilateral issue in the Balkans to one involving most of Europe,  dividing it in two main coalitions: the Triple Entente—consisting of France, Russia and Britain—and the Triple Alliance of Germany, Austria-Hungary and Italy.

assuming that by westerners you mean americans. that they were mean and controlling and abusive to its peasants.

explanation:

in 550 b.c.e. cyrus the great, the leader of the persians, conquered the medes and united the iranian people under one ruler for the first time. cyrus became the first king of the persian empire and went on to establish one of the largest empires in world.