There are many points of divergence in this one...
-Kerensky joined the Communist Party of USSR
-The Secretary General of the Communist Party of USSR is elected democratically between the high members since 1923, and until 1927.
-The 1929 crisis have been much stronger than in our timeline.
By the way, I only wrote the "alternate events".
1920-1929 Decade : the beginning of a new world
October 24th 1929 : A very strong crisis starts in the USA.
October 30th 1929 : The crisis is so strong that a Communist uprising starts in Wisconsin. Finally the president Hoover is killed and there is a huge political crisis.
November 17th 1929 : Charles Curtis is killed and the presidency is vacant. Elections are to be held
December 15th 1929 : Roosevelt wins most of the Western part of the US. The newborn Fascist Party USA wins most Confederate states, while the Socialists win most of the North. Republicans only keep New England. Roosevelt is elected president, and the second candidate is Norman Thomas.
June 1st 1923 : The Secretary General of the Communist Party of USSR is elected democratically. Stalin's Anti-Reformist Union wins the election and 327 seats at the Supreme Soviet against Trotsky's Left Opposition (250 seats) and Kerensky's Reform Movement (23 seats).
January 1st 1924 : Reform Movement's members "disappear". Elections are redone. This time Trotsky wins with 309 seats against Stalin's 291 seats.
January 9th 1924 : Stalin tries to make a "Third Russian Revolution", but this revolution fails. After the Assembly voted yes to exile Stalin.
January 1st 1925 : Trotsky wins the election (347 seats). Second is Kamenev (202 seats) and third is Bukharin (51 seats).
January 1st 1926 : Trotsky wins the election with 578 seats. Bukharin is second with 20 seats and Kamenev only got 2 seats.
January 1st 1927 : Trotsky wins all the seats of the Supreme Soviet.
January 11th 1927 : "Full powers" law. Trotsky is now at full command of the USSR. The Supreme Soviet has a minor role.
January 1st 1928 : Trotsky wins all the seats again.
January 1st 1929 : Trotsky wins all the seats again
Late 1929 : USSR is the only country on which the crisis has no influence.
1930-1939 Decade : from Crisis to War
May 1st 1930 : Communists and Socialists unite with the United Socialist Party. The USP shows support for Trotsky's government
November 14th 1933 : New elections are held. Thomas's USP wins the election, seconded by the Democrats. Republicans only got the electoral vote of Vermont.
December 1st 1933 : Creation of the International Socialist Treaty (IST) between US, Spain and USSR.
January 1st 1934 : There is a "Brown Scare" against fascism. Wallace joins the USP.
January 17th 1934 : US prepares for war against Nazi Germany.
May 8th 1935 : After a Japanese attack on Pearl Harbor, US enters the war
October 4th 1937 : US send soldiers in Europe to free France and Italy with UK.
October 10th 1937 : Thomas wins the election against Roosevelt.
September 4th 1938 : Yalta Conference
February 1st 1939 : Germany surrenders
August 7th 1939 : after atomic bombs being launched at Hiroshima and Nagasaki, Japan surrenders.
September 14th 1930 : In the election, the NSDAP's vote increased to nearly 40%, Nazis becoming the largest party in the Reichstag.
December 1st 1930 : Hitler gets full powers.
July 17th 1931 : Germany remilitarizes Ruhr.
August 6th 1931 : Trotsky reorganizes the Red Army.
October 11th 1931 : Hitler allies with Mussolini.
December 9th 1931 : Spanish Republic established.
June 24th 1932 : Anschlüss
December 1st 1933 : Spain allies with Socialist US and USSR.
October 4th 1934 : Germany annexes Sudetenland
October 7th 1934 : Hitler allies with Hirohito.
December 1st 1934 : Trotsky, Baldwin and Flandin create the European Anti-Fascist Pact.