Thomas Lubanga, a former rebel leader from the Democratic Republic of Congo, has been convicted of kidnapping children and forcing them to become child soldiers.
The Congolese warlord faces life imprisonment for his crimes, which saw children as young as nine snatched from their homes. While the boys were brutalised in military camps, trained to be vicious killers, the girls were forced to become sex slaves.
It is the the International Criminal Court's first verdict since it was set up 10 years ago as the first permanent war crimes tribunal.
The conscription of child soldiers happened in the north eastern area of the Democratic Republic of Congo, which is rich in gold reserves.
Children were engaged in the ruthless conflict of 2002 to 2003, which saw Hendu and Lendu ethnic groups clash in the Ituri region.
Lubanga pleaded not guilty to the crimes, saying that while he was Leader of the Union of Congolese Patriots, he was only a politician, and was not directly involved in the violence. However the three judges sitting on the case were unanimous in delivering the guilty verdict.
The presiding judge Adrian Fulford told the tribunal:
"The evidence demonstrated that children endured harsh training regiments and were subjected to hard punishment," AFP news agency reports.
"The evidence demonstrated that the children were deployed... and took part in the fighting," he said.
Lubanga will be sentenced at a later date, however the maximum penalty the tribunal can inflict is a life sentence.
The case is an important landmark for the ICC, the first case that focused on child soldiers as well as the first ruling for the permanent war crimes tribunal. The institution is backed by 120 countries, but not supported by America or China.
However Lubanga is just one of the war criminals for which an arrest warrant has been issued. Joseph Kony, Ugandan rebel leader and president of his Lord's Resistance Army movement in Uganda is wanted for war crimes.
More than 30,000 children are believed to have been abducted by the rebel group, with the male children being forced to bear arms, and the females being used as sex slaves. The group has also slaughtered hundreds of thousands of civilians in central Africa.