The Enclave was a pocket galaxy which connected the Obverse to the wider universe. It was home to many races, including the Glass Men of Valcea, the Sahmbekarts, the Steigertrudes, and the giant Owls.
The Enclave was the stage for a massive war that broke out amongst the various species. Daedalus attempted to bring the forces of the wider universe into the war, and sent time corridors (PROSE: The Ancestor Cell) through time and space in order to instigate conflict. Telosa, Wertherkind, Sonturak, and Skaro were planets touched by Daedalus' corridors; the Daleks were predicted to be the first "new arrivals" who would enter the Enclave's war. The Federation, the Martians, the Sontarans, the Draconians, and the Cybermen were also expected to respond to the Enclave's affairs interfering in their own.
The Eighth Doctor was present at the very beginning of the conflict, having taken Fitz Kreiner and Compassion on the Nepotist's investigation of the Enclave, but was prevented from taking part in the war by Iris Wildthyme. He never learned what happened when the wider universe closed in. (PROSE: The Blue Angel)
War Queen Romana considered the war in the Enclave and the Doctor's "jaunt in the Obverse" to be a reflection of the future War in Heaven. She used a Time-Space Visualiser to predict the events of the War before it even arrived on her Gallifrey. (PROSE: The Shadows of Avalon) One of Mictlan implied that the Enclave had actually been constructed by the Celestis. (PROSE: The Taking of Planet 5)