The Japanese were absolutely united from within by an unwavering belief that they were fighting for an immortal god king who resided amongst them and passed orders along directly to them through his human intermediaries. From coast to bloody coast, almost every single Japanese man, woman and child believed this like they believed in gravity. Dissenters and disbelievers were universally derided, incarcerated or executed. They were qualifiably homogenous in both thought and deed.
This great persuader was the Emperor Hirohito.