The Great Wyrm War was the largest war between the Dragons and the Linnorms in recorded history, after which the Dragons retreated temporarily from society and the Linnorms were sent into hiding.
The time before the Erelicia Imperium conquered Aevorea.
The Crusade was the war against King Agrimas, of Irkalla. Technically, it just refers to the counterattack made by Methuselah and the Templars, but it has come to refer to the entire war, from the time that the Humans arrived.
After the Crusade, an event known as the Restoration took place, which was an effort to remove Humans and repopulate Staerenriki with Svarts.