Hazrat Mahdi (pbuh) will appear after a great terror among people throughout the world

96- Ghaibat Nomani: It is narrated from Ibne Uqdah from Ahmad bin Yusuf from Ibne Mahran from Ibne Bataini from his father from Wuhaib from Abu Basir from Imam Muhammad Baqir (a.s.) that he said: “The Qaim will not appear except after a great terror among people, earthquakes, seditions, calamities, plague, terrible killing among the Arabs, great disagreements among people, separation in the religion and bad living until one will wish to die in the morning or in the evening, because of the oppression of people and their striving to eat each other."

(The Promised Mahdi, Allamah Muhammad Baqir Al-Majlisi, English Translation of Biharul Anwar, Volume 13 (Old Edition)/ Volum 51-52-53 (New Edition), Kitabul Gaibah-Book of Occultation, Imam Mahdi(a.t.f.s)- The Twelfth Imam of the Twelver Shia, Part II, Translator; Sayyid Athar Husain S.H. Rivzi)