Complex sentence: Towards the end of the war, a reformed Second Army fought more successfully at the Battle of Debrecen, but, during the ensuing Siege of Budapest, it was destroyed completely and absorbed into the Hungarian Third Army.
Split into simpler sentences: Towards the end of the war, it fought more successfully at the Battle of Debrecen. During the ensuing Siege of Budapest, it was completely destroyed and absorbed into the Hungarian Third Army.