A surprise Breen raid on Earth in 2375 that damaged Starfleet Headquarters, announcing the Breen alliance with the Dominion and shocking the Federation.
The Breen attack on Earth was a surprise assault carried out in 2375, during the last months of the Dominion War. Shortly after joining the Dominion, the Breen sent a force past Earth's defences and struck San Francisco, causing heavy damage to Starfleet Headquarters and killing many people.
The attack is the opening event of the episode The Changing Face of Evil and is the first open sign of the Breen alliance. It shakes the Federation, which had believed Earth to be beyond the reach of the war. Benjamin Sisko fears for his wife Kasidy Yates, and the episode follows the Dominion as it launches a counterattack to retake the Chin'toka system. The Breen use a new energy dampening weapon in the battle, and the allied fleet suffers a terrible defeat in which the USS Defiant is destroyed.
The raid on Earth marked a low point for the alliance. It also helped push the Cardassian leader Damar toward open rebellion against the Dominion in the final arc of Deep Space Nine.