The Treaty of Tyre was a truce called between the Camarilla and clan Assamite in 1496 (though some sources place it in 1493; see the note below on the Convention of Thorns). The Camarilla agreed to call off all hostilities towards the clan ("hold back its Hand from the Full and Ultimate Extinction of Clan Assamite") and stop contracting Assamite assassins, whereas the Assamites agreed to cease their practice of diablerie against Camarilla members (submitting to a blood curse levied by the Tremere to ensure this), dismantle the defences of their stronghold Alamut, and no longer work as assassins.
The Treaty followed ten years of violence and near-open warfare between the Camarilla and the Assamites, begun in 1486 when the Camarilla called a Blood Hunt against them (the first and only time a hunt was called against an entire clan). The warriors of the clan had already been striking against the Kindred of the West during the years of the Anarch Revolt, largely in retribution for the Crusades, seen by many in the clan as a gambit of the Jyhad they had long sought to avoid. Despite the bloodthirst of the warrior caste, the Assamites attacked less in open combat and diablerie than in giving advice and support to the Anarchs.
The Blood Hunt can be attributed in large part to the Great Lie of the Tremere elder Etrius, who painted the Assamites as nothing more than vicious killers and diablerists. This accusation was fed not only by politically-motivated rumours but also the actions of the Assamite warriors in Europe. Once the Blood Hunt was called, the Assamites fought all the harder, and especially after the Convention of Thorns when their Anarch allies were lured back into the fold of the Camarilla.
The conflict would likely have continued indefinitely, probably ending with the death of every Assamite in Europe, had not a lone Nosferatu been found to have somehow breached Alamut's defences in late 1495. The worrying revelation that their stronghold could be found by Camarilla agents forced the elders of the clan to sue for peace, and they agreed to the Treaty early the next year.
The Treaty of Tyre and the Convention of ThornsEdit
Many sources, mostly those which tell the story from the Assamite perspective, confirm that the Treaty of Tyre took place in 1496 as a separate event to the Convention of Thorns. Others place both in the same year. Despite most Assamite sources playing down the Convention's importance, the official text (likely genuine) of the Convention mentions the Assamites submitting to the blood curse - though, perhaps significantly, as a condition to be upheld, not one already fulfilled.
Perhaps the best way to reconcile the two is to assume that an agreement was reached in 1493 which the European warrior Assamites did not plan to honour; when the Nosferatu discovered Alamut in 1495, the elders of the clan capitulated and signed the Treaty in 1496. Camarilla and Sabbat scholars of the Modern Nights, reading of the ransom and the conditions of the Convention of Thorns, either assume they happened at the same time or do not see the Treaty at all, it being far less famous than the agreement which formed the Camarilla.