Demographics. WWII ends, you get 26 - 30 years, of a work force. The WWII generation starts to retire. Also, the factories at that point need retooling. Boom

Demographics. WWII ends, you get 26 - 30 years, of a work force. The WWII generation starts to retire. Also, the factories at that point need retooling. Boomers start to enter their 20s, and start entering the workforce.