It happened in 1946. The Soviet Union used the power to veto for the first time in the history of the United Nations. This was during the Cold War.
In a nutshell, the Cold War was the rivalry between the Soviet Union and the United States after the Second World War. The Soviet Union was a communist regime while the US had capitalist interests.
There were dozens of conflicts, some big, some small and the UN was not completely successful in preventing wars. Both the Soviet Union and the US used veto to block the other’s suggestions about various policies. By 1953, the Soviet Union had used veto more than 50 times!
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