Good to hear some talk about the WWI, pre-Yawkey era. When the Red Sox were the dominant AL team, and the Yankees were strictly 2nd division. I guess known then as the Highlanders. You never hear too much about that era these days around Fenway. There is almost no recognition of those great players. Babe Ruth, for example, is virtually ignored. He was in fact regarded as the best player in Baseball when he was a top pitcher/right fielder for the Sox. Imagine what would happen today if a player like that suddenly got "sold." Salary dumps are common, sure, but this was no salary dump. He was sold for big money.
Plus a dozen other top players also--to the Yankees and other teams. The best Red Sox players suddenly changed uniforms and became Yankees. Plus Ed Barrow, who pioneered scouting and the farm system for the Red Sox--sent to the Yankees. The result was the Yankees became Champions, and the Red Sox became chumps. There were strikes in Boston over it. All forgotten today--except for the rivalry. That started it.
The explanation for all this has always been the Red Sox owner, Harry Frazee, was a New Yorker who needed money to finance his Broadway shows. I've always suspected more than that. The upstart AL, led by Ban Johnson, wanted to establish a top team in NY to compete with the NL Giants for recognition.
The Yankees were rebuilt, with a new stadium tailored for Ruth, and a new cast consisting of some of the Red Sox best players. The result is history.