Conversation so far:
Who was the strategy against?
The chief elements of the Arab strategy, developed chiefly by Faisal and Lawrence, were firstly to avoid capturing Medina.
What was the strategy?
and secondly to extend northwards through Maan and Deraa to Damascus and beyond.

Question: Why did their enemies want to capture Medina?
Self-contained rewrite: Why did Faisal's and T. E. Lawrence's enemies want to capture Medina?