Why Washington fails without Japan

What happens if Japan refuses the Washington Naval Treaty without a 7:10 ratio or continuation of the Anglo-Japanese alliance?

The treaty probably collapses because naval limitation cannot work when one of the principal competitors remains outside it.

Participation by the leading naval states was the treaty's foundation. If Japan refuses, the central Pacific arms competition remains, removing much of the bargain for Britain and the United States. Italian absence would similarly discourage France and Britain because Mediterranean construction could continue unchecked. This logic also explains the weakness of later limitation efforts once important powers declined to participate.