Looking at the attack on Pearl Harbor, it’s tempting to say that the catalyst was the trade embargo placed on the Japan by the United States and other Allied nations. The problem with simplifying it down to that one event, however, is that it ignores the years of back and forth between Japan and the United States.

The Pearl Harbor attack wasn’t a spontaneous maneuver by the Japanese, done out of sheer anger and recklessness. Planning took months, well before the announcement of an embargo. In fact, the tension between Japan and not just the United States but also China and other nations including the United Kingdom and France dates back to the 1920s – specifically to a meeting that took place in Geneva in 1927.

During the meeting, Great Britain and the United States became bogged down trying to determine an acceptable total tonnage limit on naval cruisers. This was to be a figure that would prevent any world power having a naval force far larger than it would ever need. Though the two nations left the conference without an answer, in 1930, they met up again, this time with Japan, France, and Italy joining in.

The London Naval Conference of 1930

US delegates en route to the London Naval Conference 1930

With threat of an arms race looming, the urgent need to come to an agreement was felt by all, but that also meant there was little time for thorough negotiations, and at least one nation would be left displeased with what they were forced to agree to.

Eventually, a deal was reached where Britain, the United States, and Japan would be locked in a ratio of 5:5:3 for capital ships, meaning for every five ships that the United States and the UK had, Japan was allowed to have only three.

Already belligerent and causing friction with the United States, Japan spoke up, unhappy with the deal. Though the relationship between the Americans and the Japanese was already tense, the agreement wound up making things even worse. Japan became increasingly vocal about its displeasure with the ratio, especially considering that before the conference, it started building 12 new vessels.

The United States was initially opposed to allowing a larger ratio that would give Japan the opportunity to increase its fleet size, but it eventually conceded and the ratio was raised from 5:5:3 to 10:10:7. The treaty signed at the London Naval Conference lasted until 1936, and when the nations gathered once again in London to renegotiate terms, one key player was missing. After getting what it wanted at the 1930 conference, Japan refused to participate in 1935 for the negotiation of future terms.

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