By: Mir M.Hosseini
According to Mongol traditions, after Kuyuk died in 1248, a tent assembly was convened to elect Mangu as the new leader.Hulagu was assigned to a great new expedition to Persia. After making necessary preparations, Hulagu started from Karakorum in July, 1252. This was the second Mongol invasion of Iran with special instructions to exterminate the Assassins and the Caliphate. Hulagu was accompanied with Chinese engineers specialized in siege operations.New Mongol policy was giving promises and then breaking them with some pretext, this was the case of massacre of inhabitants of castles after they surrendered, even with written treaties that they should be spared.