What did muslim leaders and scholars do to preserve and expand knowledge and learning?

They kept all their wisdom written down and there is still their language here today to decode what they said.

Explanation:

While in Christian Europe the Greek and Roman sources of wisdom were ignored (actively or passively), Muslim leaders brought them together in Baghdad and Cordoba and translated them into Arabic. Once again, when European states were mentally prepared for this material, they could easily acquire it from the Muslims, who had kept it on in the interim.

think its caste system

explanation: