Ultimate war

What the Eleventh Doctor described as the "final, ultimate war" and The War to End All Wars was created when the Sontarans changed history. (NOTVALID: Legacy)

Sontaran Invasion
The Eleventh Doctor and Vastra arrived in Cardiff on 16 October 1978, discovering that the Earth had been prematurely invaded by the Sontarans, who have acquired time travel and are rewriting the planet's, and the entire universe's, history. The Doctor determined that he must go back through his own personal timeline to defeat them, gathering friends and companions to help him, before its too late. Vastra summoned Jenny Flint, and the three went to Hedgewick's World of Wonders during the Cyberman attack to find Porridge, to the Dalek Asylum for Rory Williams, and the Latimer Residence for Jagganth Daiki-Nagata, before moving on further through the Doctor's most recent adventures. They managed to find more companions and halt the Sontarans' operations, but along the way, they find massive paradoxes destabilising time and allowing events that never occurred to happen, such as encounters uniting the Doctors' enemies, along with some events to occur out of sequence, such an encounter with the Silence. Many other skirmishes take place, resulting in Clara Oswald joining the team in 1875 Paris, Sam Garner from the depths of New York City, and John Riddell in a forest in Scotland. Stabilising the paradoxes leads to the Doctor's previous incarnations, including his Tenth, Seventh, and Sixth selves, being sent through time to join the team.

Eventually, the Doctors and their allies fought the Great Intelligence, in the form of a glowing transparent pyramid, through its activities in London 1892, 2013, and Trenzalore, uniting with the Eighth Doctor along the way, culminating in a confrontation in the Time Vortex where it called upon Snowmen and the Ice Governess for defence, ultimately falling to the Doctors.

The Zygons
As the "lesser races"s fell to the relentless Sontaran war machine, or were wiped from history by their actions in the past, the Zygons watched as a whole generation of hatchlings burned as the winds of time consumed them. Fearing their imminent demise, the Zygons quickly launched ships carrying "thousands of brave warriors" directly at the red planet of Sontar. In the chaos every Zygon warrior died save for five. These five used their body print technology to infiltrate the Sontaran High Command, and initiated a treaty between the Sontaran and Zygon races. The Sontarans would shield the Zygons from the changes to time which were ripping the universe apart, whilst the Zygons would help prepare for a "glorious future" where the Zygon and Sontaran empires controlled the universe together.

Fending off an attack from a Sontaran flagship, the TARDIS materialised in 21st century London, only for the team to find themselves under attack by the Sontarans' Zygon allies whom served as reinforcements against the Doctors and their companions. At this point, according to the Zygons, the Slitheen had been wiped out whilst the Cybermen fled to the far reaches of time with rumours that even the Nestene Consciousness had been eliminated.

The TARDIS team pressed on, going through the events leading up to the Doctor's "death" on Lake Silencio to continue stabilising time and combating the Sontaran/Zygon threat, continuing to gather allies along the way. Further paradoxes resulted in the Third Doctor joining the team. However, time continued to collapse, leading to battles against the Weeping Angels over London, a Dalek invasion in 2024, an army of Rorybots, and an "unholy alliance" between the Church and the Daleks. The team also encountered a unique series of artificial paradoxes that appear to be the attempts of someone trying to reach them.

The Doctors began to formulate a plan, trusting in the ingenuity of humans and believing that ensuring the safety of creative and important individuals like Vincent van Gogh and Winston Churchill could limit the fracturing of the timeline. But after facing and defeating Sontaran Captain Vade the Defiant, they were told that forces greater than the Sontaran Empire were after them. Evading enemies from across the collapsing time stream, the TARDIS team followed the trace of another artificial paradox which led them into the edges of a time storm around 25 December, ensnaring them in a temporal hurricane of snowy weather.

Finally reaching the paradox, the Doctors managed to reverse the polarity of the paradox's neutron flow, allowing Jack Harkness to reach them at last. He informed them of the entry of "an old friend" of theirs into events.

Meanwhile, the First Doctor watched from his own TARDIS the full extent of the Sontarans' plans, and to his horror, the fall of Sontar as an army of Toclafane, led by the Master, overwhelmed the planet and its forces all across time at once.

The Master
The TARDIS team pushed through the time storm, confronting enemies the Doctors had fought previously at Christmastime. They realised that Captain Jack was as they witnessed the Sontarans being decimated by Toclafane, as well as from a warning message directly from the Master. They pushed onward to escape the storm, passing through the Doctor's future in Christmas and uniting with the War Doctor in the process.

Once out, they continued to run through time to evade the Master, going through through the early adventures of the Eleventh Doctor in the process. They found time to pick up some of Jack Harkness's allies such as Ianto Jones, and managed to come into contact with the Second and Ninth Doctors. They were also plagued by the generation of bubble universes in the weakened timeline, which pulled the the TARDIS into them as quickly as they were created. Observing their efforts, the First Doctor decided that it was time to join his future selves, uniting with them through a paradox surrounded by Adipose.

Not giving up on catching the Doctors, the Master continued to pursue via both his Toclafane and his own past incarnations. As the Doctors evaded the Weeping Angels in the caves of Alfava Metraxis, they were confronted by, but the TARDIS team managed to outmatch him. Later, the Master used his TARDIS to attack the Doctors through the Time Vortex, but was again bested, leaving a Sontaran Flagship in his wake that forced the TARDIS to materialise on Krop Tor in the middle of the Beast's awakening. Not long after, they faced s in a skirmish with the Toclafane in Tarminster, but would once again manage to escape.

Following a breach of Toclafane into the TARDIS interior, the Doctors realised that they needed an army to fight the Master's forces, and for that, they needed a great military leader. The decision to find the Brigadier was made, but to reach him through the weakened time stream, they needed to build a specific machine to summon him. Retrieving metal casing from a Silent ship, gears from Starship UK (where they acquired a Winder ally), a sentient lens in the form of the melted Ice Governess, and harnessing the power of the Doctor's tomb on Trenzalore, they managed to retrieve the Brigadier fresh from the 1970s/80s. But the reunion was short-lived as their actions summoned "time sundered" Whisper Men that were much more dangerous than before, forcing the team to flee back to the TARDIS. They made a blind jump through time to escape, ending up at Auderly House during the World Peace Conference, where another paradox led to the Fifth Doctor joining the team.

Betrayal and Redemption
Now aided by the Brigadier, the TARDIS team determined that they needed a weapon that could hurt the Toclafane. Martha Jones remembered a diary Alison Docherty wrote on combating them during The Year That Never Was, and the Doctors conclude that it might have ended up in their timeline at the Library. But before they could head there, the TARDIS was pulled into the relative future, bringing them to Sherwood Forest in the middle of the Sheriff of Nottingham's fight with the Twelfth Doctor. The TARDIS team helped to defeat him, and the Eleventh and Twelfth Doctors were shocked at each other's presence before the team returned with him to the TARDIS, which now took on the Twelfth Doctor's console room design.

Now up to speed, the Twelfth Doctor helped the team fly the TARDIS to the Library, fighting through paradoxes along the way that summoned the Fourth Doctor, uniting all thirteen of his incarnations. But as the TARDIS materialised, the Doctors vanished, and the doors opened to reveal Professor River Song. The older and more experienced River took the lead, guiding the companions through the Vashta Nerada into a chamber containing a wealth of books and material pertaining to the Doctor, where Docherty's diary was found. Its information proved immediately useful as the team fended off the Toclafane, the Saxon Master, and as they return to the TARDIS.

The Doctors reappeared as the team returns, explaining that a temporary snap in the timelines was to blame, and that the TARDIS should be able to prevent a more serious repeat. With the information from Docherty's diary, the Doctors determined that a tellurian transformer from a Cyberman infostamp could be plugged into the TARDIS and be able to send a shock through time to disable all Toclafane. As it was a rare piece of technology, the Doctors split up to find it. The First Doctor traveled to Antarctica and checked the invasion force from the Snowcap invasion for an infostamp, with no luck.

As the Twelfth Doctor, the younger River Song, and Clara Oswald searched the 3W Institute, they were confronted by Missy, who summoned a Cyberman army and a CyberKing to stop them. River retreated to the TARDIS to secure it while the Doctor and Clara utilised Bessie to escape the CyberKing, which gave chase through the streets of London. After evading its missiles and other attacks in a lengthy pursuit, the Doctor has River land the TARDIS into the ground with enough force to create a chasm in the street, which the CyberKing fell into. The TARDIS team departed London, hoping the others had found an infostamp. (NOTVALID: Legacy)