In cases where an entity (usually the state) has or is able to obtain custody of the hunger striker (such as a prisoner), the hunger strike is often terminated by the custodial entity through the use of force-feeding.
Fasting was used as a method of protesting injustice in pre-Christian Ireland, where it was known as Troscadh or Cealachan. It was detailed in the contemporary civic codes, and had specific rules by which it could be used. The fast was often carried out on the doorstep of the home of the offender. Scholars speculate this was due to the high importance the culture placed on hospitality. Allowing a person to die at one's doorstep, for a wrong of which one was accused, was considered a great dishonor. Others say that the practice was to fast for one whole night, as there is no evidence of people fasting to death in pre-Christian Ireland. The fasts were primarily undertaken to recover debts or get justice for a perceived wrong. There are legends of St. Patrick, the patron saint of Ireland, using the hunger strike as well.
In India, the practice of a hunger protest, where the protestor fasts at the door of an offending party (typically a debtor) in a public call for justice, was abolished by the government in 1861; this indicates the prevalence of the practice prior to that date, or at least a public awareness of it. This Indian practice is ancient, going back to around 400 to 750 BC. This can be known since it appears in the Ramayana, which was composed around that time. The actual mention appears in the Ayodhya kanda (the second book of the Ramayana), in Sarga (section) 103. Bharata has gone to ask the exiled Rama to come back and rule the kingdom. Bharata tries many arguments, none of which work, at which point he decides to do a hunger strike. He announces his intention to fast, calls for his charioteer Sumantra to bring him some sacred Kusha grass (which Sumantra won't do, since he's too busy looking at Rama's face, so Bharata has to get the grass himself), and lies down upon the grass in front of Rama. Rama, however, is quickly able to persuade him to abandon the attempt. Rama mentions it as a practice of the brahmanas.
In the first three days, the body is still using energy from glucose. After that, the liver starts processing body fat, in a process called ketosis. After depleting fat, the body enters a "starvation mode". At this point the body "mines" the muscles and vital organs for energy, and loss of bone marrow becomes life-threatening. There are examples of hunger strikers dying after 46 to 73 days of strike.
In the early 20th century suffragettes frequently endured hunger strikes in British prisons. Marion Dunlop was the first in 1909. She was released, as the authorities did not want her to become a martyr. Other suffragettes in prison also undertook hunger strikes. The prison authorities subjected them to force-feeding, which the suffragettes categorized as a form of torture. Emmeline Pankhurst's sister Mary Clarke died shortly after being force-fed in prison, and others including Lady Constance Bulwer-Lytton are believed to have had serious health problems caused by force feeding.