The two main Sudanese rebel movements signed a declaration of unity and proclaimed the year 2002 to be a year of unity for the people of Sudan.
There was jubilation and singing as John Garang of the Sudan People's Liberation Army (SPLA) and Riek Machar of the Sudan People's Democratic Front signed the declaration of unity.
The two leaders agreed to merge their movements, under the name of the SPLA, following two days of talks in the Kenyan capital, Nairobi.
A spokesman for the SPLA said all hostilities between the two groups will cease immediately and they will unite as a "single entity to resist" the Khartoum government in the north.
Committees are being set up to work out the integration of their military forces, political structures and humanitarian institutions.
Bethuel Kiplagat, a former Kenyan diplomat who is a longtime adviser to both rebel groups, congratulated the two rebel leaders on their decision to unite. "Many of us who have accompanied you for these 19 years feel that this is a very important milestone and which needs to be built upon," he said. "And we want to congratulate you for your courage, for your patience, for working quietly away until you have achieved what you have put your signature on today. Our prayer and our hope is that you will hold on to it. And we will be there around you to make sure that you do."
Mr. Machar was a leading member of the SPLA until he broke away in 1991, accusing Mr. Garang of dictatorial behavior.
At Monday's ceremony, Mr. Machar said he will not quit the SPLA again because he is satisfied with the principles enshrined in the new declaration. "In 1991, because we couldn't reach any agreement, I left," he said. "Unfortunately it cost us a lot. Now 11 years of conflict, brother fighting brother and you have a common enemy, it was so difficult. So I am happy today that this is over."
The SPLA was founded in 1983 to fight for the self-determination of southern Sudan against the Islamic military regime in the north. The conflict and famines related to it have killed an estimated two million people.