The most popular period in the history of jazz, started in the 1930s and continued on through the early 40s. The big band sound became the standard format and the “swing” dance craze was a national phenomenon. Also, worldwide importance of this genre was enhanced, if not caused, by the further technological development of the radio and recording industries. Larger ensembles consisting of 12 to16 players replaced the 5 to7 man smaller groups and written arrangements became more important than the collective improvising of Early Jazz.