How did the network of european alliances cause world war 1 to develop

Secret alliances cause many countries to join a small issue making it a big war. 

The assassination of Archduke Franz Ferdinand by a Serbian nationalist would have been a minor blip in history had there not been alliances on each side to back up the actions of Austria and Serbia. Austria's alliance with Germany gave Austria confidence to declare war on Serbia. Russia had shown support of Serbia and had declared they would back them up. However, no one knew of the alliances between Great Britain, France, and Russia and the alliance between Italy, Germany, the Ottoman Empire, and Austria. The existence of these alliances created a domino effect bringing everyone connected to the original two countries into the conflict. 

Primary sources are usually  more accurate and are written by someone who experienced it or witnessed it. secondary sources are those who heard of it after the fact that can lose details and or twist the event in a light that benefits them.