Editor's note: George Clooney is an actor and co-founder of the humanitarian group Not On Our Watch. John Prendergast is co-founder of the Enough Project and co-author of "The Enough Moment: The Fight to End Human Rights Crimes in Africa".
(CNN) -- We felt it everywhere we went in Southern Sudan last month: the possibility of war. In a camp for internally displaced people on the banks of the Nile River, we listened to people preparing for war. In the volatile flashpoint of Abyei, we saw a readiness to fight and die for freedom.
In the areas of southwestern Sudan formerly beset by slave-raiding militias, we met school kids who were ready to leave their books behind to defend their hard fought chance to vote for freedom.
After fighting for most of the 55 years since independence, the southern third of the country is finally getting the chance for its own independent state in a January self-determination referendum. But because the preponderance of oil and other valuable natural resources lies underneath Southern Sudanese soil, the ruling party in the North is loathe to let the South go without a fight.
Our point is a simple one: If one or the other party plunges the country back to a North-South war, there must be serious international consequences for that party.
We have been avid cheerleaders during these past few months for incentives to conclude a peace deal that would prevent the resumption of war. The carrots that we have supported and that the Obama administration has offered to the parties are meaningful. We also think there should be sticks waiting in the background, applied only if war resumes between North and South or if the central government's war in Darfur escalates.
More than 2 million people died during the last round of fighting between the North and South from 1983 to 2005. The ruling party in Khartoum has a history of breaking its promises, committing atrocities against its own people and pitting groups against each other in a divide-and-conquer strategy.
The situation in Darfur is already dire, with continuing aerial attacks by the air force, severely restricted humanitarian access, the arrests of human rights activists and a floundering peace process that doesn't include several of the main rebel groups.
With this track record, incentives alone are not sufficient to prepare a path to peace in the South and in Darfur, which is in the western part of Sudan. Real pressures need to be prepared as well, to be deployed only if necessary. The mere existence of potential consequences, if seriously planned, could help deter fighting.
In the past, the threat of consequences has helped produce improved outcomes. Pressures compelled the Sudanese government to expel Osama bin Laden from Sudan in the mid-1990s. They led to an end to the Khartoum government's bombing of Southern civilian targets and support for slave-raiding militias in the late 1990s. They helped drive the North and South to the 2005 peace deal that ended their latest round of destructive warfare.
Commencing a serious, multinational effort to build the necessary benefits for peace and consequences for war would help affect the calculations of the parties in the direction of peace. The fact that the Obama administration has effectively put forward a set of proposed incentives should trigger other countries to do the same. This effort to build multilateral incentives, though, should also build leverage with other countries to increase their willingness to consider real sticks in the event of a return to North-South war or an upsurge in fighting in Darfur.
There are a number of levers available.
U.S. unilateral sanctions targeted at specific war-mongering leaders could be expanded and deepened, focusing in particular on tracking and freezing assets.
Other countries could join in, targeting the spoilers in war scenarios through wider asset freezes and travel bans.
The U.N. Security Council could expand and enforce its arms embargo in Sudan. The U.S. and other governments could increase their cooperation with the International Criminal Court in pursuing further indictments against those most responsible for war crimes in the South and Darfur. Debt relief could be denied to the Khartoum regime, one of the most indebted in Africa after years of stealing oil revenues. Banking transactions could be disrupted, particularly for the petroleum sector.
These are all scarlet letters that could be placed on the shirts of Sudanese leaders who do not want them. This isn't North Korea. Sudan's leaders want more international acceptance, not isolation. The effect of sanctions is not intended to be economic; they are inherently political tools aimed at creating a penalty box for offending officials.
This is a war that can be prevented. A final diplomatic push over the next 30 days, led by the African Union and the United States, can quiet the winds of war between the North and South, as well as in Darfur. If the parties know that there will be consequences for choosing swords over ploughshares, the odds for peace can be improved dramatically.
The opinions in this commentary are solely those of George Clooney and John Prendergast.