Korean Crowds Cheer American Liberators

The video depicts the initial enthusiasm of a liberated nation, which turns to despair due to the continued presence of foreign administrators. Public opinion leads to a policy reversal, and a new flag symbolizes the end of the old regime.

What does the phrase 'the flag of the rising sun has gone down for the last time' signify?

What is implied by the statement 'A new flag takes its place'?