To what extent did the alliance system contribute to World War I?
The Alliance system in Europe is considered a cause of World War I for two reasons. First, many of the alliances of Europe were done in secret which caused suspicion and tension between the countries. The fact that alliances were done in secret also strips them of their principal benefit: deterrence. If countries realize when they are dealing with another country that the country has powerful allies on their side, they may proceed with more caution.
A second reason that the alliance system was a cause of World War I was because of the commitments associated with alliances. When one of the countries in an alliance is attacked, the other countries are obligated to support that country. So a regional ethnic conflict between Austria-Hungary and Serbia quickly escalated into a continental war with Germany, Russia, and Great Britain quickly honoring their alliances.