Here's one for you, with a POD in 1888. Note that this is really a bit of a different World War II, but I'm trying it anyhow.
1888 -- In OTL, the 'Year of Three Emperors' in the German Empire; ITTL, the beginning of Frederick III 'Frederick the Liberal' 's tenure as German Emperor. Frederick, a fan of British-style constitutional liberalism moves the German state into the British orbit, dismissing Bismarck and pushing for liberal reform from the top-down, allying the state with Britain as best he can as a buffer against France and Russia.
The reaction in France to the growing alliance of Britain and Germany is one of reaction and unease, leading to the seizure of power in 1890 by Georges Boulanger and the establishment of a proto-fascist state in France. Boulangist France reaches out to Russia in its own rearmament program while Britain and Germany reinforce ties. War comes in 1898 with the Fashoda Incident, with the Central Powers of Britain and Germany facing down the Entente of France and Russia.
For three bloody years, the Great War (1898-1901) ravages the Old World. Though President Roosevelt offers a conference to negotiate a peace in Washington, and the Centralists support the idea, the Entente rejects the offer and the war continues. Revolution in 1901 causes Russia to back out of the conflict, and a revolution/military mutiny in France likewise causes the defeat of the French forces and their eventual capitulation. With this, the Central Powers convene in Berlin to hammer out terms of a peace treaty. The British and Germans propose the creation of a 'Concert of Nations' to enforce international law and peace, and invite the United States to join. France will be demilitarized and forced to pay reparations, while the burgeoning socialist state in Russia will be, for the most part, ignored while the Central Powers focus on putting down the revolution there.
At the end of the day, a new republic is birthed in France and Russia is reorganized into the Workers' and Peasants' Social Republic of Russia (commonly the Russian Social Republic) following a bloody civil war that lasted until 1907. Britain and Germany enter economic boom periods, as does the United States, which by-and-large financed the war for the Central Powers, who were favored by Roosevelt. In 1904, Roosevelt is re-elected President over Democrat Alton Parker, and in 1908, William Howard Taft defeats Democrat William Jennings Bryan.
The 1910s are a decade of relative liberalism after the constraining Victorian period, largely as a result of the harrowing effects of the war on Western civilization. Less so in the United States, which is more culturally conservative as a result of not having entered the war itself. This all comes to a close, however, in 1912 with an abrupt market collapse sending the world economy into a spiral. The Presidential Election that year does not exactly feel the effects of the crash (though it does happen a month before the election) and President Taft manages to secure a second term. By 1913, however, unemployment has sky-rocketed across the developed world and radical political movements begin to make inroads in the First World.
The 1914 midterm elections see the Socialist Party of America make big gains in Congress, winning a number of seats and becoming a vital force in passing national legislation. In France, the Fourth Republic collapses in 1916 with the appointment of a Communist-led Popular Front government that quickly becomes a Communist-only government. The Social Republic of France is proclaimed in 1917. The Russian Social Republic's leadership quickly imposes more authoritarian control over the state itself, further consolidating old territories into the Republic and developing new economic tools to increase and modernize production.
In Britain, the Conservative Party, out of power for the whole of the 1910s, is returned to power in a landslide election that sees the Liberals fall behind the Labour Party in terms of actual seats. Frederick III's death in Germany in 1910 and his replacement by Wilhelm II leads to a more conservative element in Germany gaining ground.
France and Russia begin a program of re-armament, with the French Social Republic calling the Great Depression a result of 'capitalism's failure and imperialist domination'. Plans are drawn up for a rapid war against Germany and Britain, while demands for annexed territories are loudly made at the Concert of Nations. The 1916 Presidential Election in the United States ousts the Republicans, putting into office Democrat Woodrow Wilson with the support of the Socialists under Allan Benson. The Socialists grow in number in the Congress, and demand measures to reduce unemployment, measures that Wilson is slow to adopt as President.
The 1918 midterm elections give the Socialists second-party status in the House of Representatives. With progressive Republicans and liberal Democrats, however, they command a majority and control legislative mechanisms, forcing Wilson to co-operate despite his opposition to a good deal of the Socialist program. In 1920, the Presidential Election sees Upton Sinclair elected President and the Socialists gaining a majority in the House of Representatives.
Sinclair tries to drive a neutral course between reactionary Britain and Germany, now determined to 'abolish socialism' and communist France and Russia, both of which now seek to 'abolish capitalism'. These efforts prove fruitless however and in 1923, denial of France to the whole of Alsace-Lorraine leads to general war in Europe once again. The Second World War (1923-1929) has begun.
President Sinclair, continuing in Woodrow Wilson's footsteps, asks for 'armed neutrality' and American military spending triples, easing the effects of the Depression. Sinclair wins re-election in 1924 over William Edgar Borah (R), an isolationist and Woodrow Wilson (D) and continues the American re-armament program. Relations deteriorate with Britain and Germany, who Sinclair decries as 'capitalism's enforcers' following his re-election. British attempts to influence policy in Latin America eventually lead to blows between the United States and the Central Powers, with the U.S. joining the 'Internationale' in 1925.
The war continues for four more bloody years. Britain's naval supremacy is matched by the United States' productive capabilities and leads to the eventual negotiated surrender of the British in the spring of 1929. The war with Germany continues on until September of 1929 when American expeditionary forces help break the front lines and press toward Berlin.
The war has, by this time, taken it's toll. A new international organization, the International Forum, is established by France, Russia, and the United States. Britain, thanks to the influence of American anglophiles, is allowed a relatively easy peace, while Germany is cut into pieces and occupied. The 1928 Presidential Election in the United States saw the Socialists kicked out of office in favor of Republican Theodore Roosevelt Jr., an anglophile suspicious of the French and Russians. The seeds of the cold war between the United States and her former allies were hence sown at the negotiations...