The Central Powers win the Great European War (WWI in OTL) and imposes their hegemony over Europe: Germany, Austria-Hungary and the Ottoman Empire are the «superpowers» of the world in the first half of the 20th century, but the emergence of a new superpower could ruin the party.
Point of Divergence
In our time line, the Central Powers of the World War I only were Germany, Austria-Hungary, the Ottoman Empire and Bulgaria, instead, in this althist, the Central Powers are Germany, Austria-Hungary, the Ottoman Empire, Bulgaria with the belligerence of Denmark, the Netherlands, Belgium, Italy and China; the United States are neutral during the war. This equalizes the situation and gives the chance for the Central Powers get the victory of the war.
With the abandonment of war in Russia in 1917, Germany stabilizes the eastern front and creates the Regency of the Kingdom of Poland, a puppet state.
On the western front, France gets attacked by Italy, Germany and Belgium, in 1918 gives up.
Great European War
This war is equivalent to WWI, without the belligerence of the U.S.A.
Main article: Great European War
In 1914, Austria-Hungary declares the war to Serbia because, the archduke, Franz Ferdinand, an inheritor for the Austro-Hungarian throne was assassinated in Sarajevo by a Serbian nationalist, immediately, Austria-Hungary mobilizes his troops to the Serbian limits but Russia, an ally of Serbia, also mobilized its troops against Austria-Hungary and Germany causing a tension between the powers. Years ago, in 1900, Denmark, Belgium and the Netherlands joined to the Triple Alliance, consummating the Central Powers and increasing the German influence in Europe.
The official attacks between the alliances start on 28th July of 1914, when France invades Belgium and Luxembourg, causing the war declaratory from Germany, the Netherlands, Italy, Denmark and Austria-Hungary to France, likewise the declaratory of United Kingdom and Russia to the Central Powers.
In 1915, the war is stalled on the western front, in the trench wars. But in 1916, after a series of small German victories, the war becomes for Germany and Italy, winning battles in Mons, Flanders and Reims.
Officially, in June of 1917, only France and the United Kingdom continued fighting against the Central Powers (now two against one - with the Ottoman empire and Bulgaria). The war for the allied powers is lost and France asks an armistice in November of 1918, the United Kingdom surrenders in December of that same year.
The reason about the abandonment of Russia in 1917 during the Great European War was the Bolshevik Revolution, This revolution aims to implement a Marxist-Leninist government in the Russian Empire, that revolution reached the victory and the Soviet Union is established in 1922.
In the early 1920's and 1930's, the USSR played a not very relevant role in the world because the European colonial empires maintained their capitalist model in almost everyone (their colonies) and Germany consolidate its position as a great power, causing the Soviet isolation.
However, in the early 1940s Austria-Hungary was dissolved leaving various independent countries, This made also other European colonies (German, Italian, etc.) gained their independence between 1943 and 1956, also during this period, the USSR increased its influence and some of the many new states chose to establish a Marxist-Leninist model.
The Great World War
After the dissolution of the Austro-Hungarian Empire in 1943 and the independence era (1945-1950), new nations were formed in Europe, Asia and África. Most of these countries adopted a socialist regime due to the high influence of the Soviet Union, so that Europe and overall, the world was embroiled in a bipolarity between socialism and capitalism.
The called Great World War began in 1962 with the Soviet invasion of Europe and the Missile Crisis in Cuba. Germany, Canada, the Netherlands, France, the United Kingdom, United States and México will declare the war to the USSR one day after.
The Soviet Union never directly attacked Germany, but Poland did several military campaigns, which mostly failed. Poland was taken over by the German imperial troops in two months.
Because of the large coalition that had formed against the Warsaw Pact and its socialist allies, they opened fronts almost everywhere, but the Soviets managed to take several Canadian territories through the Alaskan territory, although these were later were repelled by the German-Canadian Army that they were parked waiting for the offensive.
Finally, in 1966 the nuclear exchange starts because no have another alternative to finish the war. The Soviet Union launched three nuclear bombs to Germany, the United Kingdom and the United States, time after, Italy, Spain and Japan too they received nuclear attacks. In response Germany, France, and the United Kingdom launched a total of seven atomic bombs at different locations in the USSR and China and proceeded to the invasion, although both sides were severely weakened, Germany and its allies managed to defeat and divide parts of the Soviet Union and China, the major powers of the Eastern Bloc, while members of the Warsaw Pact were stripped of their investments in the world, his socialist government was overthrown and forced him to pay war reparations.
The war finished in July of 1966 with the «victory» of the Western Bloc.