300
"It's the same story every year. He tells the history of Panem, the country that rose up out of the ashes of a place that was once called North America. He lists the disasters, the droughts, the storms, the fires, the encroaching seas that swallowed up so much of the land, the brutal war for what little sustenance remained. The result was Panem, a shining Capitol ringed by thirteen districts, which brought peace and prosperity to its citizens" (Collins 18).
An event (natural disaster, revolution, war, population spike, uprising, etc.) that causes society to drastically change.