First World War: 'the violent birth of the modern world'. The events that led up to the assassination are significantly more complicated, but most scholars agree that the gradual emergence of a group of alliances between major powers was partly to blame for the descent into war.
http://www.theweek.co.uk/world-news/first-world-war/59782/how-did-the-first-world-war-start
British backing of France during the crisis reinforced the Entente between the two countries (and with Russia as well), increasing Anglo-German estrangement, deepening the divisions which would culminate in World War I.
https://en.wikipedia.org/wiki/Causes_of_World_War_I
1 June 28, 1914 - Gavrilo Princip assassinates Franz Ferdinand. 2  July 28, 1914 - Austria-Hungary declares war on Serbia. 3  August 2, 1914 - Ottoman Empire (Turkey) and Germany sign a secret treaty of alliance. 4  August 3, 1914 - Germany declares war on France.
http://www.theweek.co.uk/world-news/first-world-war/59782/how-did-the-first-world-war-start
This seemingly small conflict between two countries spread rapidly: soon, Germany, Russia, Great Britain, and France were all drawn into the war, largely because they were involved in treaties that obligated them to defend certain other nations.
http://www.sparknotes.com/history/european/ww1/summary.html
According to Sheffield, the First World War began for two fundamental reasons: First, decision-makers in Berlin and Vienna chose to pursue a course that they hoped would bring about significant political advantages even if it brought about general war.
http://www.theweek.co.uk/world-news/first-world-war/59782/how-did-the-first-world-war-start
The origins of World War I, which began in The Balkans in late July 1914, defy easy explanation and remain controversial and debated questions.
https://en.wikipedia.org/wiki/Causes_of_World_War_I
This gallery provides a series of snapshots illustrating the way in which the First World War unfolded at home and abroad, and on land, in the air and over water.
http://www.theweek.co.uk/world-news/first-world-war/59782/how-did-the-first-world-war-start
The causes of the First World War are murky and much disputed, but time has led to some clarity.
http://www.theweek.co.uk/world-news/first-world-war/59782/how-did-the-first-world-war-start
When the war began both sides believed, and publicly stated, that the war would end soon. The Kaiser told his troops that they would be ... home before the leaves have fallen from the trees, and one German officer said he expected to be in Paris by Sedantag, about six weeks away.
https://en.wikipedia.org/wiki/Causes_of_World_War_I
The Balkan Wars were two conflicts that took place in the Balkan Peninsula in south-eastern Europe in 1912 and 1913. Four Balkan states defeated the Ottoman Empire in the first war; one of the four, Bulgaria, was defeated in the second war. The Ottoman Empire lost nearly all of its holdings in Europe. Austria-Hungary, although not a combatant, was weakened as a much enlarged Serbia pushed for union of the South Slavic peoples.
https://en.wikipedia.org/wiki/Causes_of_World_War_I
what event started world war 1
Decision-makers in Berlin and Vienna chose to pursue a course that they hoped would bring about significant political advantages even if it brought about general war.