Why Did Alliances Cause Ww1

One of the main reasons that started a chain reaction leading into WW1, was the alliances throughout Europe. Although in reality if the alliances weren't in effect then WW1 would not have happened, but the assassination of the heir to the Austro-Hungarian throne was the event that led into chaos. The alliances were a major part, although they would never have needed to come into play if there had not been a trigger to these attacks. Off all of the 4 M.A.I.N (Militarism, Imperialism, Nationalism, Alliances) the factor that contributed the most to the outbreak of WWI (World War I) was the alliances, because if they were not in effect there would be no trigger to start wars.
Some background on these alliances: the main countries that made the