Who used khipu, a system of recording numbers by tying knots on strings?.

The Inca people used them for collecting data and keeping records, monitoring tax obligations, properly collecting census records, calendrical information, and for military organization. The cords stored numeric and other values encoded as knots, often in a base ten positional system.

it was displayed because they had a love for war

du boi was considered a radical because he wanted the immediate end for segregation. the biggest different between him and booker t. washington is that, even though washington believed that segregation should be considered illegal, he did not believe at all that a law was needed to keep blacks away from whites and that this would be something natural (to have the races apart) for a long time until society adjusted, while du boi believe that agitation was the only way to end segregation.