The earliest and most serious failure of the United Nations involved its inability to .
a. Command widespread support in the United States
b. Preserve peace in places such as Iran
c. Prevent the Soviet Union from exercising its veto power in the Security Council
d. Control atomic energy, especially the manufacture of weapons

d. Control atomic energy, especially the manufacture of weapons.

Explanation:

The United Nations established in 1945 after the end of the Second World War had its aims and goals directed towards bringing world peace and security all over the countries.However, it has failed on many occasions. One of the earliest and most serious failure of the United Nations was its inability to control atomic energy and the manufacture of biological weapons by nations.It failed to monitor the creation of weapons of mass destruction and other nuclear ammunition after the end of the Second World War. The rise of Cold War was one such consequence of United Nations's failure to contain countries from amassing atomic energy.

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Bthreatening to ally with germany