Complex sentence: The Sfakians not only managed excellent force protection for General Phocas's troops, but they also supported him in the siege of Chandax, which fell on March 7,961 AD, marking the end of Arab rule in Crete.
Split into simpler sentences: The Sfakians not only managed to defend General Phocas' troops, but they also supported him in the very siege of Chandax. Chandax fell on March 7,961 AD, which marked the end of Arab rule in Crete.