I didn't have that question, but I recommend to put Marseille without s as the main answer. Marseilles is an alternate (and arguably erroneous) spelling in English only.
Please change the clue for the French national anthem, as it was never composed in Marseille ! it was composed in Strasbourg in 1792 and originally known as the Battle Hymn of the Army of the Rhine; it became the national Anthem called the Marseillaise only in 1795
Cologne is not part of the Rhine-Ruhr area, as it's too far south. The most populous city of Rhine-Ruhr would be Dortmund. Cologne is the most populous city of North Rhine-Westphalia though.
There are cities further north in Colombia than Barranquilla. Manaure if it's mainland Colombia and Providencia y Santa Catalina Islas if you include outlying islands
I was surprised to get two questions about the Spanish-American war. I'm guessing they're the only two in the 180-questions pool of the quiz. Not my lucky day... (Yes, I missed both.)
I'm making a similar quiz with the exact same name with 500 possible answers but I have given 2-3 clues like landmarks or something famous for it.
Can I still make it since it's pretty big and I have already gave it a lot of effort