As long as your POD presupposed the Nazi rise to power in Germany and an allied fascist state in Italy, I don't see anybody but the US (or UK) could have developed nuclear weapons in the 1940's.
But...
1914 - German forces execute the Scheifflein plan to perfection and Paris falls, France seeks peace, and Great Britain withdraws forces, eventually signing Madrid armistice in early 1915. France is forced to accept a demilitarized eastern zone, but German-English relationships dissolve into a cold war, with the naval race continuing and each side seeking global allies to counterbalance each other.
1932 - War breaks out between USA and Japan after long naval race. Great Britain formally neutral, but is favorably disposed to Japan. Seeking a counterweight to Britain, Germany offers USA use of German colonial harbor facilities in Asia/Pacific. Both USA and Germany offer support to China in its defensive war with China. France is taken over by revisionist nationalists and begins to rearm.
1934 - The Global War breaks out between the Alliance of Empires (Britain, Japan, France, Russia) and the Great Alliance (USA, Germany, China). Sweden, Italy and Ottoman Empire are neutral but favorably disposed to the Great Alliance. Spain, Serbian Peoples Union, and Argentina lead toward the Alliance of Empires.
1935 - Kaiser Willhem institute and its team of Swiss, German, Austrio-Hungarian, and Italian scientists, many of them Jewish, begin work on nuclear fission and its practical application under a grant from the German Government
1935 - US Navy suffers major setback in the second Battle of the Phillipine Sea. losing 10 dreadnoughts battleships to Japan's 2. Japan's secret investment in large heavier-than-air aircraft carriers and planes leads to complete desruction of USN rigid airship scouting force and US fleet is lured into a submarine ambush before the IJN heavy units engage. US forces in Phillipines surrender and US begins to consider separate peace with Japan.
1936 - Fearing loss of US ally and encirclement by UK and Russia, Germany steps up search for new weapons. First controlled fission reaction in Berlin. France is finally overrun by German forces
1937 - As position of Great Alliance weakened, a general Armistice signed. Armistice is considered just a break in hostlities as all recent combatants (except France which is ocupied) continue military built up against backdrop of growing economic problems.
1939 - Germany develops first fissoin bomb and announces to the world with a public test. No one else is even close to developing such a weapon and Germany uses monopoly of atomic weapons in attempt to dictate very favorable peace terms to replace armistice. Facing British resistance, Germany plants an atomic bomb by submarine at Scap flow and detonates it, destroying the bulk of the British East Atlantic/North Sea squadron. In concert with US, Germany institutes blockade of British Isles and moves troops to invasion ports threatening to bomb London next(to be continued...)