There were many causes that built up to the World War I but the main ones were imperialism, nationalism, militarism, the alliance system and the assination of Archduke Franz Ferdinand.Imperialism was a big contributor to the start of WWI because the larger countries wanted more power and wanted to build their economies bigger. Most of the countries wanted to expand to Asian and Africa to increase their wealth, so when other countries and empires wanted to expand there too, tension was created.
The Alliance System was a system in which if a country attacked another country the alliances of the said attacked country must defend them and attack to attacking country. This made a chain reaction which got every single country involved in the war.
Militarism also caused conflict because in the 20th century all the European countries were working towards gaining powerful militaries. The European countries wanted to prove to each other that they were powerful and there for could dominate the other countries.
The final and most immediate cause of World War I was the assassination of Franz Ferdinand, who was the Royal Archduke of Austria. Franz and his wife were shot and then blown up in June of 1914 in Bosnia which was part of Austria-Hungary. They were assassinated by a Serbian and this directly led to Austria-Hungary declaring war on Serbia and then because of the Alliance System most of the other countries became involved.
These are the Countries that were allies during WWI Germany, Austria-Hungary and Italy Great Britain, France and Russia Spain, Belgium, Switzerland, Netherlands, Sweden, Norway, Rumania, Serbia, Bulgaria, Albania, Greece, and Turkey