Which nation was critical of the September massacre?

French.

Explanation:

French nation was critical of the September massacre because in the month of September, mass killing of prisoners was held. This mass killing of prisoners took place in the capital city of France known as Paris which started from September 2 to September 6 in the year of 1792. It was also called the “First Terror” of the French Revolution because it occur in the period of French revolution.

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