[We were once allies with Japan after WWI, do you know what triggered them turning into an enemy? When the US cut back quotas on immigrants from Asia, the Japs considered it an insult, and it helped give rise to the militarists. ]
That was just another excuse floated by the Japanese and adopted wholesale by American academics. Should China attack countries that fail to take in Chinese immigrants? The Japanese were WWI allies because they had their eye on German territory in the Pacific. They had been expanding against the Chinese empire, and American attempts to hold that expansion back prompted Japanese hostility. In Japanese minds, it was merely doing on the Asian mainland what various Chinese rulers had done for thousands of years. Foreign opposition to that expansion was just an obstacle to be surmounted, and one excuse was just as good as another. Deeds are a better indicator of intent than words.