Bangladesh, July 11 -- France had just beaten Paraguay to continue another deep World Cup run when the conversation drifted away from football.

Celeste Amarilla, a Paraguayan senator, had posted racist remarks about Kylian Mbappe and questioned the identity of a French team filled with players of African heritage. Her comments were crude, but the argument behind them was familiar. Versions of it return whenever France reach the latter stages of a major tournament: are these players really French?

It is a strange question to ask of men born, raised and developed in France, wearing the national shirt and singing the national anthem. Yet it persists because Les Bleus have become more than a football team. They are a screen on which people...