Siege of Trenzalore

The Siege of Trenzalore was a conflict which lasted for more than 300 years initiated by a message broadcast through time and space that no one could understand.

The Beginning
The Papal Mainframe arrived at Trenzalore first and, recognising the significance of the message, created a force field around the planet to protect the small village there. Unknown to them, Weeping Angels had already arrived and hidden in the snow planetside. By the time the Doctor arrived hundreds of starships had gathered, including those of the Daleks, Cybermen, Sontarans, Slitheen, Judoon, Terileptils and Silurians (possibly the Monoids, Racnoss, and Pyroviles also participated). Mother Superious Tasha Lem assisted the Doctor and Clara Oswald reaching the planet.

When the broadcast was revealed to be the First Question, sent from Gallifrey, trapped in a pocket universe and emanating through a crack in time and space, the Doctor refused to leave the planet to be destroyed by his enemies in space, all of whom would seek the destruction of the Time Lords. However, he also wouldn't bring the Time Lords back through the crack, fearing the Last Great Time War would start anew. Tasha Lem, changing the faith of the Papal Mainframe into one of silence (to prevent the Doctor saying his name, bringing the Time Lords back and restarting the Time War), initiated the Siege of Trenzalore.

The Conflict
Over the next three centuries each of the Doctor's enemies tried various means of penetrating the force field created by the Church of Silence, each time defeated by the Doctor's ingenuity. The Daleks, however, turned their attention to the Church itself, assaulting the Mainframe, turning everyone into Dalek puppets and penetrating the field afterwards, followed by the Cybermen and the other fleets. Allying himself with the Papal Mainframe's soldiers and Confessional Priests (now known as the Silents), the Doctor repelled each attack, and eventually all had either been destroyed or had retreated save for the Daleks who continued to attack the village in Dalek Fighter Pods and a massive Dalek saucer. The Doctor, dying of old age by this time, made ready to sacrifice himself to the Daleks when he was granted a new regeneration cycle by the Time Lords through the crack in time at the request of Clara Oswald, and used his excess regeneration energy to destroy the Dalek forces, effectively ending the siege.

Aftermath
With the Daleks defeated, the people of Christmas saved and the crack closed by the Time Lords, the Eleventh Doctor retreated to his TARDIS. After an emotional goodbye to Clara Oswald, he finally succumbed to old age and regenerated into the Twelfth Doctor. (TV: The Time of the Doctor)

Alternate Timeline
In an alternate timeline the siege ended with the death of the Doctor and millions of others, turning Trenzalore into a cracked, ruined world with a giant graveyard rather than the beautiful planet it was before the Doctor arrived. The dying TARDIS remained on the surface and became the Tomb of the Doctor. (TV: The Name of the Doctor, The Time of the Doctor)