The murder of Francisco Madero and the iron-fisted rule of Victoriano Huerta that followed might seem like the end of constitutional democracy in Mexico, but in fact the revolutionaries like the ones who had overthrown Díaz took up arms once again, and the US military occupied the Mexican port city of Veracruz.
The UK and Japan had an alliance agreement, and when the Great War began, Japan was eager to enter the conflict. Aiding their ally was nice, but the Japanese were also eyeing German colonial possessions in the Pacific.
Kaiser Wilhelm told the troops they would be "home before the leaves fall." By autumn of 1914, it was clear they would not.