“Mommy, please tell me again, how did World War I begin?”

“Sweetheart, I already told you, that was long ago. A century is a very long time.”

“But, Mommy, please.”

“Well, it’s complicated. Do you really, really want to know?”

“Yes, Mom.”

“It’s a sad story. The world was organized in one way, and that way collapsed, and in the process millions of people were killed.”

“Wow. How was it organized before?”

“There were things called empires. They controlled vast territories full of different peoples, and some of these peoples wanted to rule themselves rather than be governed by a faraway emperor.”

“O.K.”

“The Austro-Hungarian Empire was one of them. It had lots of grand palaces in its capital, Vienna, where people danced at fancy balls. It governed parts of a poor corner of Europe called the Balkans where its rule was disliked. One day in 1914, the heir to the Austro-Hungarian throne and his wife were assassinated in a Balkan city called Sarajevo by a young man, a Bosnian Serb, who wanted the freedom of the south Slavs from imperial rule.”