Congolese warlord Thomas Lubanga has been sentenced to 14 years in jail for recruiting and using child soldiers in his rebel army in 2002 and 2003.
Taking into account time in custody, he will now serve a further eight years.
In March, he became the first person to be convicted by the International Criminal Court (ICC) since it was set up 10 years ago.
The conflict between ethnic groups in Ituri, north-eastern DR Congo, is estimated to have killed 60,000 people.
Lubanga led the Union of Congolese Patriots, an ethnic Hema militia which was active in the war that started in the Ituri region and its main town of Bunia in 1999.
This was a local conflict within the wider DR Congo war, which left an estimated five million people dead - mostly from hunger and disease.
The Lubanga case is closely related to the current fighting in DR Congo, where forces loyal to Gen Bosco Ntaganda are threatening the main eastern city of Goma.
Gen Ntaganda is accused of the same crimes as his erstwhile ally Lubanga and his M23 group resumed its rebellion shortly after Lubanga was convicted, amid mounting calls for Gen Ntaganda to be arrested.
During the trial, the court heard how Lubanga would go to people's homes and ask them to donate something for the war effort. He would ask for cash, a cow, or for a child to fight for his rebel army.
The court also saw video footage of Lubanga at a training camp, galvanising children as young as 10.
Another video showed young children working as bodyguards.
Lubanga was arrested in March 2005 by UN peacekeepers, along with other militiamen.
He showed no emotion as he was sentenced.
He cried as he was transferred to The Hague in March 2006.
Judge Adrian Fulford praised the former warlord for his conduct and co-operation throughout the trial, the BBC's Anna Holligan in The Hague says.
But he was highly critical of the former prosecutor Luis Moreno-Ocampo, she says, accusing him of making errors, failing to submit evidence to support his claims and allowing his staff to give misleading statements to the press.
He was also critical of the way he had used witnesses.
During the trial, the court heard from former child soldiers, including one who had been sent into battle.
When he came face to face with Lubanga in the dock, he crumbled and was unable to present his evidence.
In June, Mr Moreno-Ocampo said he was asking for a "severe sentence" of 30 years.
He said the prosecution was requesting a sentence "in the name of each child recruited, in the name of the Ituri region".
Speaking outside court, the victims' legal representative, Franck Mulenda, said he was satisfied with the sentence.
"There's a sort of public revenge, revenge of justice, because the victims couldn't have revenge on their own," he said.
But the question of compensation still needed to be resolved, he added.
Mike Davis, from the human rights organisation Global Witness, said that the sentencing of Lubanga was an "important development" but that it sounded like "a rather low sentence in relation to the crimes that he committed".
Congolese government spokesman Lambert Mende agreed that he should have been jailed for longer but said it was a "positive signal" for peace in the region.
"It's useful in teaching those who, after Lubanga, still play at being untouchable warlords," he said, reports the AFP news agency.
But Lubanga's sister, Angele Zasi, said he was innocent and did not deserve the 14-year sentence.
"Everything that has happened in the Ituri province hasn't been caused by Thomas Lubanga only," she told BBC Afrique.
"On the contrary, he saved the people of Ituri. The international community knows the reality but they don't want to be fair."
Both sides now have 30 days to appeal.