Complex sentence: Warsaw was evacuated and fell on 4 August to the new German 12th Army, at the end of the month Poland was entirely in Austro-German hands, and 750,000 Russian prisoners had been taken.
Split into simpler sentences: Warsaw was evacuated and fell on 4 August to the new German 12th Army. At the end of the month Poland was entirely in Austro-German hands, and 750,000 Russian prisoners had been taken.