Complex sentence: He found Imam Mahfuz with the sultan of Adal encamped on a plain that was surrounded by mountains; after first sending soldiers out to secure the passes, the Ethiopian Emperor closed upon Imam Mahfuz.
Split into simpler sentences: He found Imam Mahfuz with the sultan of Adal encamped on a plain that was surrounded by mountains. After first sending soldiers out to secure the passes, the Abyssinian Emperor closed upon Imam Mahfuz.