The WTS has always taught that Britain and American make up the Anglo-American dual World Power which make up the League of Nations.
Not 'always', so be careful what you tell a JW. It's better to ask a question so that if you don't get it quite right, it doesn't matter because you were only asking a question, not making a false statement.
WT 15 August 1966, p499
So the more stable governments of the earth have really advocated and supported the League. It is significant that Revelation 13:11 says that the beast with two horns like a lamb ascended out of the earth. The seventh world power is a dual one, the Anglo-American World Power, well represented by a two-horned beast. Britain, America’s joint partner in the Anglo-American World Power, was the foremost member of the League. It is true that the United States Senate voted against America’s joining the League of Nations. Nevertheless, the United States supported the image of the wild beast through its partnership with Britain and also because its then president was a strong advocate of the League. Since that time the United States has become a leading member as well as the home of the United Nations. Throughout this period of time since 1919 the United States has also given much talk to the self-determination of peoples, and to the reconstitution of nations that have been swallowed up by aggressive empires, such as Poland, Czechoslovakia, Yugoslavia, Finland, Estonia, Latvia and Lithuania. Thus national aspirations have been stirred up among subject peoples. The United States promotes the ideologies of the League of Nations.