The Second International (Socialist International) is a collection of moderate leftist political parties. For example, the British Labour Party and the German Social Democrats are affiliated to it.
The Third International was the Communist International. Commonly referred to as Comintern, it was created at the behest of the Communist Party of the Soviet Union for the express purpose of establishing Communist Parties in countries across the world. The first Communist International meeting was held in Moscow on March 2, 1917.
The Fourth International was created in 1938 by Leon Trotsky. It represents the Trotskyist strain of Communist thought, particularly Trotsky's ideas of Permanent Revolution.Second International
Third International
Fourth International