A fragment of Stalker's War Sword, a symbol of his defeat
Broken War is a sword formed from a portion of the War greatsword, the weapon given to Stalker by the Sentient Hunhow. This weapon is granted as a reward for completing The Second DreamQuest. Additional copies can be built afterwards; the main blueprint drops from the Shadow Stalker upon death or when he is forced to flee, while its other components (namely the Hilt and Blades) can drop from Conculysts.
This broken version of War deals mostly Slash damage instead of War's Impact, making it better suited against flesh.
The Broken War is a piece of the larger War greatsword, which was split in two following the climax of The Second Dream quest, with the smaller piece torn being re-purposed as a one-handed sword.
Prior to Hotfix 18.6.3, Broken War required War to craft and vice versa, making them the only two weapons to have recursive build requirements. This also meant that the only way players could own both weapons at the same time was to buy the Hunhow's Gift bundle, which includes War.