A war was a type of conflict.
According to the Kaled military officer Major Brogan, "War [did] terrible things to good people", by bringing out extremes in emotion and behaviour. (AUDIO: Innocence) The Fifth Doctor believed that "war can make monsters of the best of us". (AUDIO: Empire of the Racnoss)
The Twelfth Doctor stated wars, after massive casualties and destruction, always ended with people doing what they should have done from the beginning, which was to "sit down and talk". (TV: The Zygon Inversion)
When you fire that first shot, no matter how right you feel, you have no idea who's going to die! You don't know whose children are going to scream and burn. How many hearts will be broken! How many lives shattered! How much blood will spill until everybody does what they were always going to have to do from the very beginning: Sit down and talk!
The Third Doctor warned a Thal expedition working against the Daleks not to glorify their stories upon their return to Skaro, to avoid the prospect of war sound exciting to the largely peaceful race. (TV: Planet of the Daleks) He also acknowledged, however, "the sad truth" that war often bred progress, and that without any such dynamic, many species and civilisations risked remaining static. (PROSE: Catastrophea)
The Time Lords warred with the Great Vampires during the Dark Times. (TV: State of Decay) They also engaged in two major time wars which appeared to destroy Gallifrey: the War in Heaven against the enemy, (PROSE: Alien Bodies, The Ancestor Cell) and the Last Great Time War against the Daleks. (TV: Dalek, The Day of the Doctor) The latter conflict ended with Gallifrey and the Time Lords being shunted into a parallel pocket universe. When the Time Lords attempted to leave this realm, it caused the Siege of Trenzalore with the various races of the universe fearing a second time war. Through a force field established by the Papal Mainframe, the Eleventh Doctor enforced an uneasy truce. (TV: The Time of the Doctor) Viewing this situation as an "endless, bitter war", (TV: A Good Man Goes to War) the Kovarian Chapter attempted to prevent the Doctor from reaching Trenzalore but ultimately ended up ensuring that he would. When the New Dalek Paradigm conquered the Church, the Siege turned into an open war, one that lasted centuries. (TV: The Time of the Doctor)
Earth had at least six world wars: Two in the 20th century, (TV: Twice Upon a Time, PROSE: Timewyrm: Exodus) two between the 20th and 25th centuries, (AUDIO: Frostfire) one in the 37th century (COMIC: Art Attack) or the 49th century (AUDIO: Singularity) and one in the year 5000. (TV: The Talons of Weng-Chiang; AUDIO: The Butcher of Brisbane) The Ninth Doctor mentioned he was present at World War V. (TV: The Unquiet Dead)
After the First Doctor helped defeat the Daleks during the First Dalek War, his granddaughter Susan stayed on Earth with resistance fighter David Campbell. (TV: The Dalek Invasion of Earth, Prelude Deceit) In the centuries that followed, the Dalek Empire waged a further series of wars, labelled as the Dalek Wars, against the galaxy. (PROSE: The Whoniverse) The Daleks also warred against the Mechanoid Empire, (COMIC: Impasse) and fought against the Movellans. (TV: Destiny of the Daleks) The Dalek Empire eventually collapsed into the Imperial-Renegade Dalek Civil War, causing the Daleks to begin losing their campaigns against alien forces. (AUDIO: Innocence) At its onset, the New Dalek Paradigm sought to wage war on many rival empires but was consistently foiled in its efforts by the Eleventh Doctor. When Oswin Oswald deleted all information about the Doctor from the Pathweb, the Paradigm's war efforts ground to halt as they attempted to make sense of their memories. When they regained their memories of the Doctor via turning Tasha Lem into a Dalek puppet, the Paradigm declared war on the Doctor at the Siege of Trenzalore. Historians who succeeded the conflict believed, though were not certain, that the Paradigm had devoted the entirety of its army to this war and that their defeat had been the final fall of the Daleks. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)
Just prior to invasion of Earth by the New Dalek Empire in 2009, General Sanchez, director of UNIT's base in New York City, announced "ladies and gentlemen, we are at war!" (TV: The Stolen Earth) Similarly, in the face of an attack on the Game Station by the Daleks in the year 200,100, Jack Harkness announced "this is it, ladies and gentlemen, we're at war!" (TV: The Parting of the Ways)
Throughout the history of the universe, the Cyber-Wars were a series of conflicts where the Cybermen sought to upgrade all of humanity. (TV: Nightmare in Silver) The last known of these conflicts saw the fall of the Cyber-Empire and the near extinction of both humanity and the Cybermen. (TV: Ascension of the Cybermen)