"At least one scholar sees the period from collapse of the Ottoman Empire through the decline of Arab nationalism as time of relative unity and harmony between traditionalist Sunni and Shia Muslims - unity brought on by a feeling of being under siege from a common threat, secularism, first of the European colonial variety and then Arab nationalist.
A remarkable example of Sunni-Shia cooperation was the Khilafat Movement which swept South Asia following the defeat of the Ottoman Empire, the seat of the Caliphate, in World War I. Shia scholars "came to the caliphate's defence" by attending the 1931 Caliphate Conference in Jerusalem. This was despite the fact they were theologically opposed to the idea that non-Imams could be Caliphs or successors to Muhammad, and that the Caliphate was "the flagship institution" of Sunni, not Shia, authority. This has been described as unity of traditionalists in the face of the twin threats of "secularism and colonialism."
Another example of unity was a fatwa issued by the rector of Al-Azhar University, Mahmud Shaltut, recognizing Shia Islamic law as the fifth school of Islamic law. In 1959, al-Azhar University in Cairo, the most influential center of Sunni learning, authorized the teaching of courses of Shia jurisprudence as part of its curriculum."