Would the United States stay out of the war?

Could the Tsingtao war remain a conflict between Britain and Japan without American intervention?

Possibly at first, but probably not for long: if either Britain or the United States fought Japan alone, the other risked seeing its own position in East Asia weakened by the outcome.

Immediate American entry is not assumed, though prolonged neutrality appears unlikely. Britain and the United States share an interest in preventing Japan from defeating the other Western naval power in East Asia. A Japanese victory over one would leave the survivor facing a stronger regional opponent and a diminished bargaining position. Decades of naval cooperation also give the two services a basis for working together. Intervention follows from balance-of-power logic and established ties rather than the later Tripartite Pact or the alliances of 1941.