Ben Affleck is an actor, writer, director and the founder of the Eastern Congo Initiative, a U.S.-based advocacy organization.

Last week, a heavily armed rebel militia, M23, took control of the eastern Congolese city of Goma, the economic center and capital of the country’s North Kivu province. Unfortunately, to those of us who work in eastern Congo, the only surprise in this turn of events was how little attention it received.

Two years ago, almost to the day, I wrote in The Post about the bloodiest war since World War II and its continued toll on the Congolese people. From 1998 to 2003, eight African nations fought on Congolese soil, killing millions, forcing tens of thousands of children to become soldiers and, in some areas of Congo, subjecting as many as two of every three women to rape and other forms of sexual violence. Violence continued long after combatants agreed on a cease-fire. With regional war looming once again, it is time for the United States to act.

President Obama is well acquainted with this crisis. During his career in the Senate, he authored the Democratic Republic of Congo Relief, Security and Democracy Promotion Act. The president should appoint a temporary envoy to signal clearly that finding a lasting solution is a priority for his administration. Past models for this approach — sending Sen. John Kerry to Sudan, veteran diplomat Richard Holbrooke to the Balkans or Gen. Colin Powell to Haiti — demonstrate that high-level diplomatic intervention at the right moment can cut through deadly impasse and open the path toward lasting stability.

As a major humanitarian and foreign assistance partner in central and east Africa, the United States has significant diplomatic influence with the key players in this conflict. The Obama administration should leverage this influence first and foremost on behalf of an immediate cease-fire.

The ongoing violence is creating a massive humanitarian crisis, with tens of thousands driven from their homes in the last few weeks alone. The U.N. High Commissioner for Refugees has not been able to reach most of the camps for internally displaced people in North Kivu, where Congolese are going without food, water and access to much-needed medical care. Talks among regional leaders are underway, and the M23 rebels have recently said they would withdraw from Goma. But high-profile pressure from the United States can help stop the fighting and allow humanitarian aid to reach the people who desperately need it.

A cease-fire must be brokered immediately, as the concerned parties strive for regionwide solutions that could stop this cycle from repeating itself. The temporary U.S. envoy should work with the United Nations and the African Union to lay the groundwork for serious regional talks.

International negotiation is critical, because regional actors have not demonstrated a willingness to set aside their own interests in favor of lasting peace. Evidence is mounting that neighboring countries are providing aid to M23. Here again, the United States has unique influence with the leadership in Rwanda, Uganda and Congo; Washington must now leverage that influence to demand full withdrawal of all military, logistical and financial support to the rebels.

Within Congo, too little has changed since the last cease-fire: The country’s dysfunctional national leadership shows little interest in protecting its people from internal chaos and external interference, leaving the Congolese vulnerable to warlords’ whims. Without competent military and law-enforcement institutions, Congo’s territory will continue to provide safe haven to armed groups who prey on civilians and disrupt economic development. It does not need to be this way, and the United States can help.

In April, more than 300 Congolese and international civil organizations published a detailed report on the urgency of establishing competent, professional military and law enforcement institutions. This report made specific recommendations and received high-level attention from the policymaking establishment in New York and Washington, but there has been little follow-up.

Security-sector reform in Congo is now imperative. The United States should prioritize reform in its engagement with leaders in Congo’s capital, Kinshasa, and the incoming secretary of state should escalate that engagement considerably. Congolese President Joseph Kabila must be persuaded to accept technical assistance from the State Department. The Obama administration should coordinate support for this reform plan among Congo’s international partners, including other African countries. The U.S. Africa Command can and should help with restructuring and training Congolese forces.

After decades of violence, the people of Congo deserve peace, and the United States is in position to help them find it. As President Obama shapes his foreign policy agenda for his second term, 70 million Congolese will be watching. So will we.