It means supreme power or authority it depends on how you are using the word
At the final moments, and the subsequent end, of the Vietnam War, the South Vietnamese tried to flee Vietnam and get asylum in neighboring countries and the US (the North Vietnamese forces had won the conflict).
They've faced many problems when fleeing the country due to many reasons, including the local climate, diseases, and the region's geography. Many perished trying to scape, while others died due to ambushes and traps made by the North (during and after the war to attack American soldiers or traitors/opponents of the North Vietnamese regime).
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