In 1923 the German philosopher, Oswald Spengler, published his masterpiece, The Decline of the West, of which World War I was the first chapter. He did not live long enough to witness the second chapter of the decline, World War II, or the third chapter, the Cold War between the Soviet Union and its satellites and the United States and its allies. That event covered the forty-two years between 1947 and 1989, when the Soviet Empire collapsed, followed by the breakup of the Soviet Union itself in 1991. The Cold War was, in essence, World War III, and included very hot war episodes, such as the Korean War and the Vietnam War.
All-in-all, the three world wars of the twentieth century covered fifty-two years, more than half the century. The remaining forty-eight years included the great depression of the 1930s and several episodes of rampant inflation. In other words, as Spengler would have said, the twentieth century saw the beginning of the end of Western Civilization, so painstakingly built-up over centuries on the twin pillars of Judeo-Christian religious morality and Greco-Roman civil ethics.