When World War I ended in 1918, the U.S. economy began to slump. Millions of soldiers came home from the war and had to compete for jobs. Many companies that had supplied wartime goods went out of business or had to lay off workers.
The economic slump lasted about 2 years, then it leveled out and began to rise. From 1922 on, the economy soared and did extremely well for most of the decade.