Your troops will return into Catacombs without attacking or besieging of a hostile Castle or Hamlet in the following cases:
1. Your opponent has activated Total Protection over his Castle.
2. Your opponent has relocated his Castle to another place on the global map.
3. The targeted Hamlet had depleted before your battle squad has arrived to capture it.
4. Your units will return to the Catacombs without attacking a Hamlet if your opponent loses his control over it. Please note that it is impossible to attack a Hamlet which isn't controlled by any player.
Many players use such a tactic to minimise their losses: when the player who keeps the Hamlet notices that the Hamlet was attacked several times, he recalls his reinforcements remaining it unclaimed.