European nations formed alliances in the years prior to World War I to protect themselves and to increase their military and diplomatic power. Alliances are agreements made between states to provide an element of security for the nations involved. These agreements can either bind states to defend each other if one or more of them are attacked, or the alliance agreement can be based on members holding to a position of neutrality if and when conflicts develop.
The practice of forming powerful alliances that would eventually lead to the outbreak of World War I in 1914 began during the 18th century as a result of nations banding together to either promote or prevent the aims of Napoleon Bonaparte. Seven anti-Napoleon alliances were formed during the years 1797 and 1815 and involved major European powers of the time, such as England, Austria, Prussia and Spain. By the second half of the 1800s, new and shifting alliances were developing between major powers. They eventually settled into two opposing power blocs whose binding alliances meant that, if hostilities broke out between two nations, it could result in a war between all of them.
The formation of alliances between states is based on the balance of power theory. The theory's premise is that security is heightened when military strength is distributed in a manner in which no single nation has the capability of dominating the others. The practice of forming alliances is part of ancient history as pointed out by the 18th-century historian David Hume in his "Of the Balance of Power." The practice resurfaced as a foreign policy goal in Europe when the rulers of Italian city-states began to group into power blocs, such as the Italic League in the 15th century.