War prediction

War predictions were predictions of the destruction of Gallifrey in a war. Despite the Time Lords being unable to observe their own future due to the Protocols of Linearity, throughout their history, multiple parties were able to guess at Gallifrey's future. (PROSE: The Gallifrey Chronicles, The Book of the War)

Matrix prophecy
The generation of Time Lords before the Doctor's amassed enough information to glean something of their future. They knew that a spate of attacks would strike Gallifrey, one by one. These would include Omega, the Sontarans, Tannis, Faction Paradox, Varnax, Catavolcus, and the Timewyrm. A single Time Lord would be central to all these events, and Gallifrey would survive each attack. (PROSE: The Infinity Doctors, The Gallifrey Chronicles)

However, Gallifrey would nevertheless fall in a war against an implacable enemy, who would be unknown until Last Contact was made. Then, the one Time Lord would find the Lost Scrolls of Rassilon and lead Gallifrey from the darkness.

The president and members of the Supreme Council knew this prophecy, but they kept it hidden, fearing that Gallifrey would fall into chaos if it was widely known. (PROSE: The Gallifrey Chronicles) The council was split on whether to tell the Matrix to look for threats matching the description, since such action might inevitably lead to contact and conflict with the enemy. Deliberation on the topic took several millennia. (PROSE: The Infinity Doctors)

The Doctor was aware of this prophecy. His student Larna (PROSE: The Infinity Doctors) shared it with the renegade Time Lord Ulysses, his human wife Penelope Gate, and the immortal Mister Saldaamir at the Shoal. (PROSE: The Gallifrey Chronicles) Larna would later assist a renegade Time Lord called "Daniel Joyce" with his research in San Francisco. Saldaamir, a close associate of the Doctor's father, (PROSE: Unnatural History) also came to live in San Francisco. (PROSE: Beige Planet Mars)

When Padrac became Lord President and gained access to the Matrix, he saw that in every projection of Gallifrey's future, the Time Lords were destroyed by war, attrition, or collateral damage in the battles of other species. The only scenario in which Gallifrey survived was the one where the Time Lords were the only race in the universe. To achieve this, Padrac founded the Doom Coalition, who planned to use the Crucible of Souls to convert all the universe's energy into regeneration energy, making the Time Lords immortal while destroying the universe. (AUDIO: The Crucible of Souls)

At date index 309456/4756.7RE/1213GRT/100447TL, the Matrix projected that the Vore were a potential candidate for Last Contact, and a conflict with Gallifrey would result in fatalities of 20-40% of the Time Lord population. As a result, the Supreme Council mandated that no Time Lord was to engage the Vore or come within one parsec or one century of any of their moons. Marnal said that the Klade, the Tractites, the Ongoing, and Centro all had the power to destroy Gallifrey, but none of them would dare. (PROSE: The Gallifrey Chronicles) The Doctor speculated that those same groups were responsible for the Effect, along with the Nibblepibblies. (PROSE: The Infinity Doctors)

The Hybrid
In 2002, Sam Jones told Griffin about a Gallifreyan prophecy concerning a hybrid. She said the Doctor was a hybrid, his father a Time Lord and his mother a human, and that he was destined to unite the two races and "bring good old human niceness into their alien society." Though she thought she was bluffing to stall Griffin, the Eighth Doctor later asked her who had told her about the prophecy. (PROSE: Unnatural History)

The Twelfth Doctor later revealed that all prophecies in the Matrix concurred that the Hybrid of two warrior races would conquer Gallifrey and stand over its ruins before unraveling the Web of Time, destroying a billion billion hearts to heal its own. He went on to say, "The Hybrid is me." Ashildr suggested that the Doctor was the Hybrid because he was half-human. (TV: Heaven Sent, Hell Bent)

The Imperator
After ten millions of years of stasis on the Homeworld, inexplicable anomalies appeared in the breeding engines. This was interpreted by some as the Homeworld's acausal reaction to the events-to-come. (PROSE: The Book of the War)

The Imperator was one such anomaly, and he pushed for the Great Houses to drop their non-interventionist policies and become involved in the outside universe in preparation for an inevitable upcoming conflict. He also founded the Order of the Weal, run by his friend and disciple, Chatelaine Thessalia. (PROSE: The Book of the War, The Return of the King) Though the Order eventually turned on the Imperator, Thessalia used it as a vessel for her own plans and preparations.

Thessalia believed that the Homeworld's enemy would be motivated unambiguously by a racial-survival agenda and mainly concerned with maintaining the integrity of its own history. She also expected the first attack on the Homeworld to be aimed at its noosphere, with physical fighting only occurring in the final stages of the war. In anticipation of this, she commissioned the babels as a defence. (PROSE: The Book of the War)

Greyjan the Sane
Greyjan the Sane was the shortest-reigning Lord President of Gallifrey. Before becoming President, he researched the patterns of time. He believed that a law like chaos theory governed paradox. This research led him to foresee the War in Heaven, and he invented a plan for creating backup Gallifreys. He was publicly perceived as a prophet of doom.

He also researched the origins of life. Observing the common physical and chemical characteristics of all life, he theorized all living things in the universe were descended from a single "ancestor cell". However, before that cell, other organisms existed with exotic and alien biochemical systems, and by feeding off TARDIS pollution and the energies of temporal paradox, these cells would be able to grow into life that was impossible for the Time Lords to fathom and utterly inimical to their existence, which would eventually destroy Gallifrey. This theory drove him to suicide after only three years in office.

After his death, his sciences were outlawed and declared arcane, though Romana III would later build his Nine Gallifreys. (PROSE: The Ancestor Cell)

Romana
After the Doctor rescued Charlotte Pollard and began the anti-time infection of the Web of Time, the Matrix started to break down. Upon entering its projection of the future, the Doctor saw a Gallifrey choked with smog and ruled by Imperiatrix Romana. The planet was part of "the empire of Zagreus", engaged in a ruthless five-dimensional war against any perceived threat to the Time Lords' supremacy. (AUDIO: Neverland)

After the Doctor visited the Enclave, (PROSE: The Blue Angel) the Time Lords began monitoring the war there and noticed reflections of a conflict in their own future. This drove Romana to regenerate into a harsher incarnation and become War Queen of Gallifrey. She created the Nine Gallifreys and instructed her servants to seek out and capture Compassion with brutal means because she knew that Gallifrey would use type 103s in their future. (PROSE: The Shadows of Avalon)

During Romana's final term, an anomalous singularity appeared centred around Earth. It grew exponentially, draining energy from the universe around it and twisting space-time out of shape. The pre-cogs, Time Lords who channeled the timelines to predict Gallifrey's future, began to see the same future in every timeline: a future where Gallifrey had fallen and the Time Lords had never existed. (AUDIO: Intervention Earth) Shortly thereafter, a war broke out. The Watchmaker said this war would inevitably end in the destruction of Gallifrey. (AUDIO: Enemy Lines)

Irving Braxiatel
Upon hearing rumours of a threat against Gallifrey, Irving Braxiatel planned a scheme to preserve the Time Lord biodata archive so he could reconstruct Gallifrey after its inevitable fall. (AUDIO: Panacea) After Braxiatel stopped Romana II from regenerating, saying her next incarnation had sent him to prevent a horrible war, the Watchmaker said that he needed to choose to remain on Gallifrey with the knowledge of what was to come, or to hide himself away forever. (AUDIO: Enemy Lines)

At some point in his timeline, Braxiatel began preparing the planet Maximediras as a new homeworld for his people. (AUDIO: Resurrecting the Past) After he discovered that the Deindum were destined to replace his people as the most advanced time-travelling species in the universe, he tried to prevent them through time travel and, when that failed, all-out war. (PROSE: Present Danger)

The War King
81 years before the outbreak of the War in Heaven, the Homeworld's most infamous criminal and renegade surrendered himself to tell the then-President his knowledge about the Houses' future enemy. The President didn't believe him, so five years later, the renegade returned and addressed a Closed Session of the ruling Houses. They pardoned him of his crimes, but the President was still in denial, so the renegade left the Homeworld for forty years to prepare defences. Upon his return, the ensuing drama with the Faraway Declaration culminated in his promotion to the High Council under Lord President Umbaste. He immediately took action, appointing the first Academician for Game Logic and commissioning the 90-form timeships.

Umbaste would later open his biodata to the caldera in an apparent attempt to gain insights into future events. It launched him into a fugue state, his body just a husk while his mind travelled through the meta-structure of history. When he resurfaced over a year later, all he could do was repeat the word "One". The Book of the War said that he eventually committed suicide, (PROSE: The Book of the War) but Mr. Smith said that the secret minutes of House Dvora revealed who really killed Umbaste. (AUDIO: A Labyrinth of Histories)

After Umbaste's death, the renegade became the Homeworld's the War King, and he immediately began preparing defenses and developing the House Military in preparation for the War. (PROSE: The Book of the War)

The Event
The Eighth Doctor had a vision of the Enemy's first attack on Gallifrey. In it, the three oceans boiled away and the northern hemisphere's great mountain ranges were levelled. However, the Time Lords then went back in time and razed the Enemy battle-worlds before the attack could happen; the Enemy then countered this strike by using a star-killer to retroactively destroy the systems where the Time Lords had found the materials used to construct their fleet. (PROSE: The Ancestor Cell)

The Rivera Manuscript, written by a renegade of the Great Houses, told of the narrator's imprisonment by an unknown power and the results of his forced exposure to a high dosage of praxis. The account seemed to predict the enemy's first invasion of the Homeworld, first targeting the noosphere before poisoning the breeding-engines and unleashing the Homeworld's sun. Chatelaine Thessalia also predicted that the enemy would first target the noosphere.

When the enemy invaded the Homeworld at the start of the War, the predictions of the Event were avoided thanks to the defences that the War King had prepared. (PROSE: The Book of the War)

Miscellaneous
When the Eremites began their "Hegira" at the beginning of history, they believed that they would return in the Homeworld's moment of greatest need to defend and scourge the planet before seizing power. (PROSE: The Book of the War)

Several groups fled at first foresight of the War: the goddesses Time, Life, and Fate left the Spiral Politic; (PROSE: Hark! The Herald Angels Sing) the cat people vanished from the Homeworld at the beginning of the Imperator's rule; (PROSE: The Return of the King) and the Celestial Intervention Agency preemptively removed themselves from time, becoming the Celestis. (PROSE: Alien Bodies)

The Accord foresaw a "great war spreading through time". They feared that the 1970s and 1980s, which had been temporally weakened due to the Doctor's frequent visits, would be damaged, so they tried to reinforce those decades by altering the time DNA of every person who lived through those decades so that they subconsciously realised that there were inconsistencies with history. (PROSE: The Enfolded Time)

Narvin said that all Time Lords had "felt in [their] bones" that war was coming for generations, a fact which he described as a collective premonition. The only questions were "when" and "how". (AUDIO: Celestial Intervention) Years before the outbreak of the Last Great Time War, he sent Valyes to Skaro to commission the Fourth Doctor to preemptively strike at the Daleks in their earliest history. (AUDIO: Ascension, TV: Genesis of the Daleks) In the Tomorrow Window, the Eighth Doctor saw visions of Time Lords in a turquoise cathedral and of a flying saucer standing over a ruined city being patrolled by Daleks. (PROSE: The Tomorrow Windows)

In the years immediately before the War in Heaven, some Homeworlders started calling the Diaspora of the Eremites the "First Diaspora" in anticipation of a great Second Diaspora after the enemy's destruction of the Homeworld. (PROSE: The Book of the War)