Torture - there are several types
1. Punitive .........[extralegal sentence]
2. Coercive .......[to confess, recant, betray]
3. Preemptive ....[of thought outside permitted bounds]
4. Exemplary .....[discouragement of potential followers]
5. Scientific .......[when Reichsbildung is serious business]
6. Sadistic ........[pure low-brow fun]
... but whatever the immediate motivation, when performed systematically for reasons of state, the first four factors predominate as part of a violent control system.
In a morally decayed proxy-Empire which boasts of water-boarding someone 183 times in a month (== once every 4hrs, with each session lasting probably 3.75) and videotaping the whole series for later private psychostroking, only the politically purblind refuse to see that #2 is highly significant, and the confession extracted will serve its purpose irregardless of whether it is in fact true or false.
Given the circumstance of the Pentagonvernment's vengeful hardon to destroy WikiLeaks by any means necessary, it is patently obvious that the maltreatment being meted out to Manning is mainly designed to force him to 'grass-up' Julian Assange on a conspiracy charge, thus enabling the extradition of a vanguard Resistance leader by a willing vassal state [Britain, Sweden or Australia] to a certainly nasty doom.
It is a great credit to the character of Manning (the latter-day Vanunu) that he is resisting this rotten scheme at great personal cost and urgently incumbent upon those who value human- above apparatus-rights to ensure he is soon relieved or at least his martyrdom not be wasted.
I am Spartacus!
 As Hitler immortalised the agonies of July 20th 1944 conspirators, strung up on piano-wire in meat bunkers while he nursed a perforated eardrum.
 As in the case of Ibn al-Shaykh al-Libi, rendered to Egypt by CIA in 2002 and tortured until he 'confessed' the fantasy WMD connections between al-Qaeda and Saddam Hussein, which his tormentors used, amongst other assorted lies and forgeries, to 'justify' the war-crime of aggression against Iraq. [ http://www.andyworthington.co.uk/2009/04/29/even-in-cheneys-bleak-world-the-al-qaeda-iraq-torture-story-is-a-new-low/ ] After a restful spell in Gitmo, he was repatriated and murdered by 'suicide' in 2009 in a Libyan jail cell by the collaborateur Gaddafi as a personal favour to GWB, within days of being 'discovered' by Human Rights Watch.