The alliance system was formed in the aftermath of the Napoleonic Wars to maintain a balance of power in Europe. The main alliances were the Triple Alliance (Germany, Austria-Hungary, and Italy) and the Triple Entente (Britain, France, and Russia). These alliances were designed to deter war by ensuring that each country had a powerful ally to support it in the event of conflict. However, the alliances also made it more difficult to resolve disputes peacefully, as each country was reluctant to back down from a position that might have led to war.
Imperialism
The European powers were also competing for colonies and resources around the world. This competition led to increased tensions between the powers, as each country sought to expand its empire and protect its interests. The alliance system exacerbated these tensions, as it meant that each country's conflict with another power could quickly draw in its allies.
Militarism
The European powers were also engaged in a arms race, as each country sought to build up its military strength in preparation for war. The arms race created a sense of insecurity and fear among the powers, as each country worried that it would be left behind in the event of conflict. The alliance system made the arms race even more dangerous, as it meant that each country's military buildup was seen as a threat by its allies.
The alliance system was a major long term cause of war in World War 1 because it created a web of alliances and entanglements that made it difficult to resolve conflicts peacefully. The alliances also made the arms race more dangerous and increased tensions between the European powers. When war finally broke out in 1914, the alliance system ensured that it would quickly spread to involve most of the major powers in Europe.