One of the very earliest regulations regarding broadcast came about from the Berlin convention. In 1903 the nation of Germany sponsored a "preliminary conference concerning wireless telegraphy..." They treated it as a developing technology with a frightening level of foresight. Thomas H. White summarized it thusly:
"Although the conference found some areas of agreement, there were still unresolved disputes, especially about intercommunication between stations owned by different companies. "The Conference ended as many do.. by calling for another conference to clear up the issues left unresolved at the conclusion of the first conference. That sequel convened in 1906. The result of that second conference was impressive. Much of the document regarded shito-to-ship and ship-to-shore transmissions. the document also formed the International Wireless Telegraph Convention aka (Convention Radiotélégraphique Internationale) effective July 1, 1908. the pdf is here.
Also crucial but overlooked is the implication that telegraph lines, whether on land or submarine, were of neutral jurisdiction. It's conceptually complicated but the 1910 Grafton book of International law immediately grasped the ramifications. Essentially it brought into civil law that which had been declared under the Hague convention.
"Submarine cables, connecting belligerent with neutral points, were liable to such treatment outside of neutral jurisdiction as the necessities of war might require, though at the close of the war damages might be assessed...Submarine cables connecting an occupied territory with a neutral territory shall not be seized or destroyed except in the case of absolute necessity. They must likewise be restored, and compensation fixed when peace is made."The story gets twisted. The U.S. Representatives that attended the conference signed the agreement in 1906. Actually in the document they're called plenipotentiaries... But the U.S. Senate did not ratify it for another 6 years. Just in time to ramp up for WWI.