Answer :
Khmer Rouge took over Cambodia and persecuted its enemies.
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The event that led to genocide in Cambodia was when Khmer Rouge took over Cambodia and persecuted its enemies.
Why did Khmer Rouge took over Cambodia?
As a communist group, they intended to take over Cambodia to establish a one-party rule, abolish Western ideas and private property.
Hence, their decision led to the genocide in Cambodia as they persecuted scores of their enemies.
Therefore, the Option B is correct.
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