What was the Hatt-i-Humayun?

Answer 1

In 1856 the Ottoman Empire issued the Hatt-i Humayun. It's purpose was to create an Ottoman national citizenship for all people in the empire. It was not entirely successful and for twenty years there were serious efforts to make the 1856 reform decree a reality.

Answer 2

The Hatt-i-Humayun was an Ottoman declaration passed in 1856 in order to end the Dhimmi Status of Non-Muslims in the Ottoman Empire, mostly at the prodding of the British and French Empires.

While the Dhimmi Status was certainly a critical part of Islamic Law and Islamic Society through most of Islamic History (600s to 1800s), the Dhimmi Status was eventually abolished in the mid-1800s by the Ottoman Caliph.

In 1839, as part of the Tanzimat Reforms in the Ottoman Empire, Caliph Abdulmecid I issued the Hatt-i-Sherif of the Gulhane. In this document the equality of rights was generally recognized. Later in the Islahat Hatt-i-Humayun of 1856, Abdulmecid I, reaffirmed and clarified the guarantees of the equality to all subjects regardless of religion. This was supposed to create relative equality between Muslims and Non-Muslims. While it was not successful in that endeavor, it did abolish jizya and dhimmi system up to the present day.
The failure to create true equality is understandable. The Dhimmi peoples had been historically treated like second-class citizens. Improving their legal conditions did not change the man-on-the-street's view of the Dhimmi person. This is similar to how Amendments 13, 14, and 15 did not suddenly make former enslaved African-Americans truly equal to Whites. Some argue that even with the Civil Rights Movement, true equality has not been achieved. As there was never any corollary to the Civil Rights movement in the Islamic World to push for true equality between Muslims and Non-Muslims, the Islamic World remains in this intermediate stage between Dhimmi and Equality.