Why did Gombrich believe this a little history of the world would be so challenging to write?

The correct answer to this open question is the following.

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Ernst Gombrich wrote his book "A Little History of the World" in 1935. In 2001 he committed to writing the book in English for his American and English readers because he wanted to use simple terms so kids could understand the historical events such as the first humans on the planet to World War 1. The problem was that Walter Neurath, his publisher, pressed him to end the book just in six weeks in order to publish it as soon as possible. That is why he thought it was too challenging to write.

the answer is aristophanes comedies.