Why did Frank Sinatra join Tommy Dorsey’s band in 1939?

Frank Sinatra joined Tommy Dorsey’s band in December 1939 because he received a more lucrative offer than the one he had while performing with the Harry James band.1

At the time, Sinatra was a young singer whose reputation among industry musicians was growing rapidly. Recognizing the opportunity for Sinatra's career, bandleader Harry James graciously released him from his contract to allow him to accept the position with Dorsey. Sinatra subsequently spent nearly three years with the Dorsey band, a period he later credited as a major influence on his own musical phrasing and breath control.12