Four factions of South Sudan's former warring parties and political rivals have finally formed a transitional government of national unity to administer the world's youngest nation for the next two and a half years. This comes eight months after a peace agreement was signed in August 2015 to end 21 months of civil war. The civil war was caused by the power struggle between President Salva Kiir and his Vice President Riek Machar, leading to the sacking of Machar in 2013. Since the two antagonists came from different tribes, the fighting often ran along ethnic lines. Restoring Machar to the position he had held until 2013 was an important condition of a peace agreement reached last August but repeatedly violated. Last week there were again fears of an imminent collapse of the peace process because Machar did not or could not return to the capital on April 18 as planned. This was because of a dispute over the number of troops and types of weapons that could be brought to Juba along with the rebel leader and his general chief of staff. The US had to threaten sanctions or an arms embargo on South Sudan's leaders if they failed to cooperate in a proposed unity government to end the bloody conflict. Machar was sworn in as vice president in the national unity government on Tuesday after he returned to Juba from his base in neighboring Ethiopia. The new government will oversee a transitional period leading up to elections in 30 months' time. It will also set up a hybrid court to try those accused of the worst atrocities, as well as a national healing and reconciliation program. Last week's developments provide a ray of hope but too much rejoicing would be premature. Elections and the hybrid court may cause a rift among the ruling factions. The relationship between Kiir and Machar even before the split was never smooth, giving the impression that they were essentially running separate systems within the government. There were shouts of joy at the airport as supporters greeted Machar but there was no obvious warmth when Kiir and Machar greeted each other. Newspaper reports speak of visible hostility between government and rebel troops at the airport when Machar arrived. Integrating rival military forces into one body is essential if South Sudan is to avoid future conflicts but this is easier said than done.This means that the US as well as regional countries and the West who brokered the peace deal should not think their mission is over with the formation of the unity government. Washington which was the main backer of South Sudan's independence from Sudan has a vital role to play in this respect. South Sudan leaders should place their country's interests above their personal ambitions. Violence has killed more than 50,000 people and forced more than 2.2 million from their homes including about 600,000 who have sought refuge in neighboring countries. United Nations agencies warn of famines as civilians die from hunger. Some 2.8 million people — a quarter of the country — need aid while thousands face starvation in northern areas hardest hit by violence. The economy is in very bad shape, with foreign reserves rapidly diminishing and inflation growing. The war has made things worse. Oil production that stood at 245,000 barrels per day is down by roughly a third. The drop in global prices has hit South Sudan hard as oil is its main source of revenue. There is no need for South Sudan which fought a costly and protracted civil war from 1983 to 2005 to win independence from Sudan to become involved in another destructive internal conflict.