The Crusades, World War I, World War II and September 11th all were of extraordinary importance in the course of human history, and each centered around acts of violence. Many of the most memorable and transformative events from the world's history have violence in common.
The Crusades were a series of military conflicts between Christian soldiers and Muslims inhabiting the Middle East. The First Crusade began in 1095 with a sermon delivered by Pope Urban II. The goal of the Crusades was to return control of the Holy Land to the Christian Church. Over the next 200 years, numerous other crusades occurred, seeking to take control of more and more of the land the Christian Church felt entitled to as followers of Jesus.
World War I began with the 1914 invasion of Belgium and France by Germany following the assassination of Archduke Franz Ferdinand, the heir to the Austro-Hungarian Empire. Major European powers, including Britain, soon became involved, as did the United States. At the end of the war, the empires of the Russians, Germans, Austro-Hungarians and Ottomans collapsed and seven new European nations formed. Almost 10 million soldiers died in the war and 21 million sustained wounds.
World War II was responsible for the death of 17 million soldiers. The war began in 1939 when Germany, led by Adolf Hitler, invaded Poland. Allied with Italy and Japan, the Germans fought against Britain, America and other allies. Over 70 countries in total had some involvement in the war.
On September 11, 2001, 19 men hijacked four jetliners. One plane each crashed into each of the two World Trade Center towers, causing their collapse. Another plane crashed in a Pennsylvania field, while the fourth was flown into the Pentagon. Nearly 3,000 peopled died in total.