Manning, who faces a possible 154-year jail sentence, has offered to plead guilty to several offenses but he denies prosecutors' most serious charge -- that he knowingly aided the enemy, chiefly Al-Qaeda and Osama Bin Laden.
The trial follows an exhaustive series of preliminary hearings that outlined the government's case against Manning, 25, over leaks of diplomatic cables and war logs that caused huge embarrassment to the United States and its allies.
His opponents, however, contend that he is a traitor whose behaviour wantonly endangered the lives of people around the world, including US citizens.
The lengthy nature of the case against Manning -- he was arrested in May 2010 while serving as a military intelligence analyst near Baghdad -- has revolved around the complexity of the charges he faces and his treatment in custody.
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His legal defence team successfully argued that he had been subject to unduly harsh detention methods from US military personnel and, consequently, he will receive a 112-day reduction of any eventual jail sentence.
It is that charge that Manning disputes, though the soldier admitted in testimony earlier this year, an unauthorised audio recording of which was later published online, that he did in fact pass a huge cache of files to WikiLeaks.
He said he did so to start a public debate, but the military judge hearing the case, Colonel Denise Lind, has warned she will not allow Manning's trial to turn into a wide-ranging forum on the rights or wrongs of US foreign policy.