The league nation was established to maintain peace but it failed as ______
A ) the United Nations organization was established.
B) the second World war broke out in 1939
C) the first world war ended
D) the cold war started between the USA and USSR.

Hint: League of nations was a world wide intergovernmental organization.After the Paris peace conference held in 1919, league nations were founded.The League's nations had different sets of goals like prevention of the war , improving global welfare and also settling disputes.

Complete answer:
United nation organization established: founded in 1945 after the World War ll they have an agenda to maintain international peace and security developing friendly relations with nations also they promoted social progress, better living standards and human rights.The UN replaced the League of Nations.it aimed primarily to spread peace.
Second World war broke out in 1939:
The failure of the League of Nations was the primary cause of World War II.The onset of the Second World War made it clear that the League had failed in its primary purpose.
First world war ended In 1919:
The Versailles treaty officially ended the WW1.The Treaty also established the League of Nations to prevent future wars.
Cold war between USA and USSR:
Since the 1930 cold war came into existence.it was the most important political issue of the early postwar period. It grew out of disagreements between the Soviet Union and the United States.
So, the correct answer is option B.

Note: In the month of September in 1939, Hitler took over Poland from west; 2 days later, France as well as Britain declared war on Germany, beginning World War II.Stalin's forces then moved and occupied the Baltic States .