Complex sentence: The gap was closed on 21 August, trapping 50,000 German troops, but more than a third of the 7th Army and nine of the eleven Panzer divisions had escaped to the east.
Split into simpler sentences: The gap was closed on 21 August, trapping 50,000 German troops. But more than a third of the 7th Army and nine of the eleven Panzer divisions had escaped to the east.