Less than two weeks after they seized the city, the rebels withdrew, the result of heavy international pressure, doubts about whether they could hold and administer a major city and the promise of negotiations with the government. They left waves of assassinations and disappearances, lootings and carjackings in their wake.

The loss of a major city, even temporarily, humiliated the government. Abroad, it reawakened fears of a return to the dark days after Mobutu Sese Seko’s ouster in 1997, when militias and foreign armies rampaged across the country.

The government revamped the officer corps in the east. “So far the army seems to be better behaved,” said Ida Sawyer, a senior researcher in Congo for Human Rights Watch, though she said there were still abuses and accountability was lacking for the spree of rapes. “It seems that they have gotten very clear instructions from the top of the hierarchy and that seems to be filtering down.”

In March, the United Nations Security Council authorized a new intervention brigade that would, according to its mandate, take “all necessary measures” to protect civilians. The United Nations also brought in the new force commander, Maj. Gen. Carlos Alberto dos Santos Cruz, who had won praise for his assertive, even aggressive posture in Haiti. An internal document described his goals as to “recapture the initiative” and to defeat “emerging threats.”

Many analysts say that the mandate has always given peacekeepers the authority to use deadly force to protect civilians, and that what was needed were more aggressive commanders.

“There’s been a lot of hype about the intervention brigade, some of it justified, some of it not so justified,” said Jason Stearns, an author, blogger and Congo expert. “It’s a matter of interpretation. Others have chosen to interpret the clause in the mandate very loosely, very passively. The new force commander thinks it means to take pre-emptive action, disarm before events occur.”

The rebels had pulled back just a few miles outside Goma and continued to shell the city. In August, when the fiercest fighting began, Congolese forces were backed by the new peacekeeping brigade, including air support from Indian helicopters. Lt. Col. Olivier Hamuli, a spokesman for the Congolese military, described the fighting as “eight days without stopping, day and night.”