Alliances played an important role in WWI because, there were two main alliances in Europe the Triple Alliance: Germany, Austria-Hungary, and Italy, and the rivals Triple Entente: the Soviet Union, Britain, and France. These alliances are what caused the war to rise rapidly from what should have only been regional conflict into a war throughout Europe.
The Alliance system was a key factor in the causation of WWI. Germany was scared because it was surrounded by two rival allied powers, France and Russia. Great Britain joined forces with Russia and France because it feared a Germany, the system of alliances between Europeans in the early 1900s helped in causation of WWI by causing a relatively small conflict, this was because, first, the alliance system gave the courage to some nations to act more aggressively and, second, that nations step up to defend their allies and this start the conflict which helped to cause WWI.
Alliances are possibly the best known cause of World War I. An alliance is a formal political, military or economic agreement between two or more countries. Military alliances usually contain promises that during war, one country will help the others. It can also include financial backing, like the supply of materials or weapons and, military mobilization and in declaration of war. Alliances may also contain economic elements, such as trade agreements. By 1914, the Great Powers of Europe had shuffled themselves into two alliance.
To wrap it up, Alliances played a big role in WWI and helped to start the war. Alliances helps countries to rise and have a better army and economic, but some country use wrong and start being more aggressive and this could lead to war and disaster and could cause destruction to the country and its alliances.