What is the origin of the ritual of Ashura?

I am currently reading the following paper

An Attempt to Trace the Origin of the Rituals of ʿashūrāʾ

I thank the brother who has made the paper available to me (you know who you are).

This paper is not written by a Shia. From the look of it, the author may not even be a Muslim.

On a personal level, I have always been interested to find out the origin of some of the ritual associated with the Day of Ashura. Ashura is the 10th of the Month of Muharram. The most famous event that happened on the 10th of Muharram is the event of Karbala. This is perhaps one of the saddest day in the history of Islam and Muslims because on this day in the year 680 CE, the Grandson of the Prophet of Islam, Hussayn son of Ali (may peace be on him) was slaughtered mercilessly with his children, his brother, his nephews, his friends and his extended family while the female members of his family (sisters, daughters and wives) looked on with horror.

Hussayn (may peace be upon him) is the son of Fatima (may peace be upon her). Fatima is the beloved daughter of the Prophet Muhammad (may peace be upon him and his family). Hussayn (as) with his brother Hassan (as) are leaders of all men in Paradise.

Both of these honorable men (grandsons of the Prophet) were killed by the order of the first and the second king of the Ummayad (the first dynastic family to run the Muslim empire).

The paper starts with highlighting the division in the Muslim Ummah.

1. Supporters of Muawiyah (Lanatullah)
2. Supporters of Ali (may peace be upon him)

The author then mentioned that remembrance of Imam Hussayn (as) and the event of Karbala is one of the main distinctions between the Sunni sects and the Shia.

To the Shias, the martyrdom of Imam Hussayn and his loyal family and friends it one of the ultimate sacrifice and as such the Imam, apart from being the leader of all the men in paradise, is also the leader of the martyrs (arabic: Sayyid al-Suhadah).

Please continue reading part 2