Answer with Explanation:
<em>I can see that there are no choices.</em>
The event which preceded the outbreak of the First World War was the assassination of "Franz Ferdinand," the person who was supposed to inherit the<em> Austria-Hungary throne.</em> He was a close friend of Kaiser Wilhelm, the last German emperor. His assassination occurred while he was having a city tour in Saravejo.
Such<em> insolent crime</em> made Austria-Hungary enforce its authority by preparing for a war. Emperor Franz Josef then asked for help from Kaiser Wilhem by writing a letter. It was successful in having Germany's full support.
Then, Austria-Hungary demanded Serbia to<u> wipe-out terrorists within its border</u> due to the assassination of Franz Ferdinand. This was actually an <em>ultimatum</em> and that if they didn't act fast, they will have to face a<em> military action.</em><em> </em>
Serbia then asked help from the Russian government. The Russian troops were started to be mobilized against Austria-Hungary.