It seemed like a good idea at the time. That’s the explanation I come up with for why World War I started.
Virtually the entire world became embroiled in war due to one disorganized act of violence in Serbia against the Austro-Hungarian Empire. The assassination of Archduke Ferdinand and his wife was the politically small spark that lit big militaristic hopes and expansionist dreams.
WWI historian David Stevenson said on CBC’s Sunday Edition that negotiation and compromise could have averted war. No one imagined it would be a four-year-long worldwide bloodbath. Would they have been more cautious if they had?
According to Margaret McMillan in The War that Ended Peace, the 19th century had been peaceful between nations in Europe. Conflicts were internal, distant or between specific nations. General war in Europe was not something even the eldest person alive in 1900 had experienced. There were no memories setting off warning bells.

In The Guns of August, Barbara Tuchman quotes the former German Chancellor in 1916 saying, “How did it all happen?” Then-Chancellor Bethmann-Hollweg replied, “Ah, if only one knew.” During the Cuban Missile Crisis of 1962, having recently read Tuchman’s book, President John F. Kennedy told his brother Bobby that he didn’t want somebody writing that about him in years hence. He reached a settlement with Russia. A veteran himself with a brother killed in WWII, Kennedy had memories of war.
A Family War

WWI was a family war, not just for those with loved ones fighting, but for the protagonists. The heads of the three major participant nations were cousins. Kaiser Wilhelm II and King George V were grandchildren of Queen Victoria, as was Tsarina Alexandra of Russia. The mothers of George V and Tsar Nicholas II were sisters. The Kaiser and Tsar were 2nd cousins. All had been friends since childhood. But once declarations of war started, they couldn’t help each other.
Nations piled in like a bar fight. To help friends, attack enemies, make a score, settle a score. Some had no choice: imperial powers immediately brought in their colonies. Very few remained neutral.
The end of every fight might lay the seeds for the next. The terms of peace in 1919 made The War to End All Wars become The War that Caused World War II. It also redrew the world’s map, ended monarchies, birthed the Soviet Union and led to the end of colonialism.

The valour of those who fought and those who mended the damage got done what had been started. But most likely they all asked themselves the Chancellor’s question, “how did it all happen?” The estimated 16 million military and civilian war dead never got an answer.