You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Genghis_Khan

Context:
In the early 1990s the memory of Genghis Khan with the Mongolian national identity has had a powerful revival partly because of his perception during the Mongolian People's Republic period. Genghis Khan became one of the central figures of the national identity. He is looked upon positively by Mongolians for his role in uniting warring tribes. For example, it is not uncommon for Mongolians to refer to their country as "Genghis Khan's Mongolia", to themselves as "Genghis Khan's children", and to Genghis Khan as the "father of the Mongols" especially among the younger generation. However, there is a chasm in the perception of his brutality. Mongolians maintain that the historical records written by non-Mongolians are unfairly biased against Genghis Khan and that his butchery is exaggerated, while his positive role is underrated.

Question:
What do some Mongolians feel non-Mongolian historians exaggerate about Genghis Khan?

his brutality