Complex sentence: Thousands of Sarajevans lost their lives under the constant bombardment and sniper shooting at civilians by the Serb forces during the siege, the longest siege of a capital city in the history of modern warfare.
Split into simpler sentences: Thousands of Sarajevans lost their lives under the constant bombardment and sniper shooting at civilians by the Serb forces during the siege. It is the longest siege of a capital city in the history of modern warfare.