History will damn the persecutors of Bradley Manning. Big powers who hide crimes away from their own people – while claiming to act in their name, of course – fear few more than those determined to hold them to account.

No wonder Manning was subjected to what the UN special rapporteur on torture, Juan Mendez, described as cruel, inhuman and degrading treatment: left languishing in solitary confinement for months, regularly stripped naked, forced to sleep without darkness, deprived of any right to privacy. An example had to be made of a soldier who helped strip away the humanitarian pretences of US power, and revealed a far uglier reality.

Although it is Julian Assange – hiding from sex allegations in London's Ecuadorian Embassy – who has dominated the WikiLeaks story, Manning is the real martyr of the story. One of the videos released gave an insight into the horror of the US-led war in Iraq: an Apache helicopter shooting dead 11 Iraqis in a Baghdad suburb, none of whom returned fire. Among the dead was a 22-year-old Reuters' photojournalist Namir Noor-Eldeen; two children were brutally wounded. The crew laughed as they massacred: the video was one striking example of how occupations corrupt the occupier.

The US military may well succeed in locking away Manning, possibly for good. But whatever the verdict, for millions, he has already been vindicated.

"For me this seemed similar to a child torturing ants with a magnifying glass," was how Manning put it. According to WikiLeaks, this exposure had a key role in forcing US withdrawal after the Iraqi government stripped US forces of legal immunity.

Manning had a noble and courageous purpose: in his own words, to "spark a domestic debate on the role of our military and foreign policy in general".

It is a debate often suppressed with the cynical manipulation of patriotism. But it was the Republican President Dwight D. Eisenhower who warned: "In the councils of government, we must guard against the acquisition of unwarranted influence, whether sought or unsought, by the military-industrial complex. The potential for the disastrous rise of misplaced power exists, and will persist."

It is exactly this power that Manning has challenged, and at great cost to himself.

Although Manning has pleaded guilty on 10 counts – such as unauthorised possession of sensitive material – he has proclaimed his innocence on "aiding the enemy", or specifically al-Qaida. In truth, it is a charge that successive US governments are guilty of: by funding and arming Islamist radicals in the 1980s, and pursuing a foreign policy that has helped radicalise millions since.

Manning faces spending the rest of his life in jail. It is not a sacrifice that should be made in vain. The fight for open, accountable international diplomacy must be stepped up in response. The US military may well succeed in locking away Manning, possibly for good. But whatever the verdict, for millions, he has already been vindicated.