The USA in the twentieth century By facebooker_2194179187487206 1917 USA declares war on Germany The USA did not want to get involved in World War I, but finally declared war on Germany Period: 1920 to 1929 Booming decade with a lot of new inventions 1929 The great depression 1939 World War II Broke out in Europe Dec 7, 1941 Japanese attacks Pearl Harbor The USA joins the war on the side of the Allies.
