The City's Bones
The Last War was a conflict raging between Aundair, Breland, Cyre, Thrane, and Karrnath along with all of their satellite nations. Its purpose was to reunite the kingdoms of Galifar after they were divided with the death of Emperor Jarlot. The conflict lasted over a century and ended inconclusively after the destruction of Cyre in the Day of Mourning. This lead to the Treaty of Thronehold that temporarily suspended the conflict until the cause was discovered.
Some people say that the war happened because of the Five Nations becoming so different form each other. Other say it was the leaders themselves that help the flame of war burn. Thalin of Thrane wanted to spread the faith of The Silver Flame. Kaius of Karrnath thought that his sister Mishann of Cyre was too weak to hold the throne. Wroann of Breland wanted a change from the old ways. But were they pawns of other powers? The Blood of Vol, The Lords of Dust, and other shadow forces all could have helped the war get started.
The War did give birth to the nations of Valenar, Darguun, and the Eldeen Reaches, as they broke away for the nations that once protected them.
Across Khorvaire, the land has been physically damaged, but there are also psychological scars. The biggest of these psychological scars is The Mournland. The Mournland is what is left of the nation of Cyre, which was destroyed on the Day of Mourning. This has left people across Khorvaire scared that similar fates might befall their own nations.
The Five Nations still hate each other. The Karrn hate the Thrane because of their earlier offensive and the Thrane hate the Karrn because of their use of undead. Aundair hate those of the Eldeen Reaches for breaking away.