An issue that was recently touched upon in another thread, but perhaps deserves its own place to be discussed in some depth:
In a TL where Italy sides with the CPs (who have all the OTL members as well; Sweden, Netherlands, Romania, and Spain optional) and America remains neutral, leading to CP victory in 1917, would some ATL equivalent of the Washington Naval Treaty exist ?
Assume that:
Japan starts in the Entente (which otherwise includes Britain, France, Belgium, Russia, Serbia, Portugal; Romania and Norway optional), but later bows out with a compromise peace or switches sides and attacks Russia when the Entente starts to collapse.
Russia gets a B-L peace, may or may not keep Belarus and Ukraine, and goes Communist and international pariah as usual.
France is crushed with a harsh Versailles peace, and besides their various severe territorial losses, reparations, and land military limitations, they are forbidden to own capital ships and submarines.
A-H collapses and is partitioned by the other CPs in mid-late 1920s.
Britain gets a relatively lenient peace: no reparations, no military limitations, they lose a few colonies (and might be compensated with French and Portoguese ones) but the bulk of their empire remains intact.
For reference, you may find two different versions of the peace treaty for this scenario
here and
here.