For all practical purposes, the Japanese control over the Northern Marianas started in 1914 when the German garrison surrendered. Though the ‘legal’ status was subject to the protracted debates and treaty negotiations around the close of World War I, the Japanese acted like their claim was legitimate from the beginning. They immediately started surveying the islands for economic development. A sparsely populated set of islands far away from the trenches of Europe while four massive empires were collapsing,1 dozens of countries were being created,2 and the League of Nations was being created simply was not a priority for the power-brokers at Versailles and DC.
After the initial push to assist their British ally at the beginning of the war, their direct involvement in the Great War was limited until a secret agreement in 1917 when the British again asked for naval assistance from the
ir Pacific Allies. This time, they needed assistance escorting convoys and engaging the Central Power unrestricted submarine warfare in the Mediterranean. The Second Special Squadron consisted of fifteen surface vessels, primarily battleships and destroyers. They came from Japan through the Suez Canal and almost certainly surprised the hell out of whoever they encountered. They assisted with several operations critical to the Allied success, notably saving nearly 3,000 lives when they rescued most of the troops being transported by converted ocean-liner SS Transylvania after it was torpedoed. Though it was a secret agreement, the English agreed to repay the Japanese assistance by supporting their claims in Micronesia.
In America, domestic partisan politics by hardheaded party leaders had frustrating consequences for the nation.3 They had assumed that, since USA possessed Guam and had been substantially more instrumental in the defeat of the Central Powers than the Japanese, the remainder of the Marianas would be reunified with the biggest island as it had been for three centuries. However, Senator Henry Cabot Lodge scuppered the ratification of the Treaty of Versailles as part of his personal beef with egghead Woodrow Wilson.4
Ironically, just six days before Japan was rewarded with official recognition of its control over Micronesia, Lodge claimed in the Senate that:
"The provisions of the Treaty of Versailles, which aim at destroying the naval and military power of Japan, will, if enforced, simply leave us face to face with the greatest military power in the world, and one that is not friendly to us.”
Here is referring to the Soviets, not the Japanese. Because of his opposition, the USA never became a part of the League of Nations and had no seat at the table when they awarded the islands to Japan, meaning that the future belligerents -separated primarily by a massive ocean - now controlled territory just a few dozen miles apart.
The Austro-Hungarian, German, Russian, and Ottomon empires
Czechoslovakia, Yugoslavia, Poland, Austria, Hungary, Estonia, Latvia, Lithuania, Finland, Iraq, Syria, Lebanon, Transjordan, Palestine.
This is familiar.
Though Wilson is considered a racist blowhard now, at the time he was considered an effete soyboy with unrealistic dreams of world peace. Lodge was the Massachusetts Harvard Republican, Wilson the Southerner Democrat. Alignments really change over time.