Are the only short term causes to World War 1 the assassination and the alliance system?
In a sense, there were only two short term causes that caused the outbreak of World War I. Yet, only looking at the assassination, and the Triple Entente and Alliance will not fully explain the short term causes. The assassination of Archduke Franz Ferdinand was a result of high tensions in the area. Serbia was very interested in gaining independence and freedom from Austria/Hungary, they wanted Bosnia and Herzegovina to join with them to create the Slavic Union. When Austria/Hungary annexed both countries, it caused tensions to rise. Serbian nationalists were appalled by these actions and felt Austria/Hungary was trying to control them.
As for the alliances, it was not as simple as the Triple Entente and Triple Alliance. There were also secret alliances and support systems that came into play as the countries went to war. The Ottoman Empire and Germany secretly allied themselves, while Russia told Serbia they would support them against Austria. Also, the British promised Belgium that they would protect their neutrality. This meant if another country attacked Belgium, Britain would come to their aid. These alliances, although they seem small compared to the others, caused other countries to spring into action once war was declared.
Even though there may be only a few short term causes, they are just as important as what effected the war long term. All of these causes led to a devastating war and changed the dynamics of countries and their relationships across the globe.