Looks like that little Clemson is jelly.

Fubuki didn't actually work around any treaties the Washington treaty limited cruiser size, but not total numbers and said absolutely nothing about destroyers. It was simply a matter of need and priority really the US and UK had built vast fleets of destroyers during WWI to counter U-boats. These fleets dwarfed the Japanese (and everyone else really) one of the time and were in fact much larger then either one needed in peace time, many were almost immediately mothballed. There was fairly little incentive for either to build more during the 20s, at least in the opinions of the politicians holding the purse strings.

Japan and other smaller navies however hadn't really radically expanded destroyer production during WWI so didn't have a sudden glut of DD that made adding more a tough sell. There was nothing much technically astounding about Fubuki it was just somewhat bigger then older ships, but not otherwise particularly innovative arguably it's biggest innovation was the enclosed turret on a destroyer as meager as that is. Nor was it like only Japan had this idea Italy had built large destroyer/tiny cruisers as far back as WWI and built more during the early 20s France also built ships of around the same size at the same time. All three nation were thus launching destroyers close to 2,000 tons at around the same time though as an increasingly militarist state with a strong expansionist sentiment Japan was building the most by a fairly wide margin.

The US had in fact specifically opposed any tonnage based restrictions on smaller warships like Destroyers at the conference that lead to the first treaty. In the end though despite several proposals it was never able to get bigger ships authorized during the 20s time period. However the situation had changed by the 1930 naval conference as the depression had begun and pretty much everyone was eager to limit everything to prevent arms races in any category. It was only then that tonnage limits both individual and total on DD were set, with an exception made that Japan could keep it's existing large destroyers,but construct no more until and if they went back under the percentage limit set for large destroyers/leaders within the total tonnage.

Interestingly and not often talked about though is that this was not universal, France and Italy would not sign onto to the new ratios that included these clauses. While they remained bound by the older Washington treaty limits on battleship tonnage and cruiser size, they never ratified the London limits on DD or cruiser tonnage. This was why for instance France was able to build a number of very large destroyers during the 30s. That said France having it's own economic issues with the Depression and Italy simply lagging in industrialization meant neither was really in a position to exploit this much beyond being free to build large DD if it wanted too.