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