What was the impact of the European alliance system on mobilization and commitment of forces leading to World War 1?

During World War I, the impact of the European alliance-system on mobilization and the commitment of military forces was, in a Word, decisive. Responding to calls for help from allies already involved, several major nations (especially Germany) entered the war much sooner because of the strict requirements for victory -- which depended almost exclusively on the mobilization-schedules for each.