Complex sentence: Alexander II of Russia gave the Hochbergs a herd of wisent in 1864 or 1865, and they roamed the lands of Pless until the German Revolution in the aftermath of the First World War, when the herd was broken up and reduced to three survivors by poaching.
Split into simpler sentences: Alexander II of Russia gave the Hochbergs a herd of wisent in 1864 or 1865. They were kept in Pless until the German Revolution in the aftermath of the First World War, when the herd was broken up and reduced to three survivors by poaching.