How were World War I and the Prohibition Movement connected?
The nationwide effort to make alcohol illegal had been gaining strength for years, and by the time the 18th Amendment passed, 26 states had already made it illegal. World War I may have added the final motivation for the country and most importantly, the Congress, to finally act and make it official with an amendment.
The two main arguments the Women's Christian Temperence Movement and the Anti-Saloon League used as far as World War I was concenred was that 1) A drunken soldier was the Kaiser's best friend and ally, and 2) that the brewing and distilling industries in America used enough barley to make 11 million loaves of bread per day for our soldiers and allies. So the portrayal of prohibition and temperence as acts of patriotism helped create the ideal conditions for passage of the 18th Amendment.