Changing Navies as a Trust-Building Tool
Possibly the most important aspect of the London Treaty is the effect it had on collaboration and trust between the eventual victorious Allied powers. Although by 1936 a second round of treaty negotiations had lost Japan and Italy as signatories, Britain, France, and the US all joined in to set restrictions on battleship size and armament.
The danger of conflict between two of these three powers was, contrary to common perception, very real during the Interwar Period. The US was isolationist at the time, but very suspicious of British domination of much of the world. France and Britain had remained allied in World War I, but the historic rivalry between the two on land and at sea had not been forgotten. And Britain for her part was cognizant of the growing industrial power of the United States, which had declared its intention to build a navy "second to none." To some British military thinkers, this was a danger almost as great as that of German rearmament - especially as there had been a real and large movement that supported the US joining the First World War on Germany's side in the First World War.
Tensions like these may seem petty in retrospect, and certainly were. However, wars have come out of even more ridiculous fears and speculative anxiety. National pride, fear of the shifting balance of power, and old rivalries comprised a significant part of the fabric of the pre-1914 environment.
But the London Treaty went a long way towards mitigating the growth of any hostility between these powerful states. Participation and compliance on the part of each signatory reinforced a sense of trust and fair play which was not found between, say, Japan and the United States. This facilitated cooperation as the international environment degraded in 1938 and 1939 on the eve of the outbreak of war.