The campaign can be divided into three phases: April was a month of PAVN advances; May became a period of equilibrium; in June and July the South Vietnamese forces counter-attacked, culminating in the recapture of Quảng Trị City in September. On all three fronts, initial North Vietnamese successes were hampered by high casualties, inept tactics and the increasing application of U.S. and South Vietnamese air power. One result of the offensive was the launching of Operation Linebacker, the first sustained bombing of North Vietnam by the U.S. since November 1968. Although South Vietnamese forces withstood their greatest trial thus far in the conflict, the North Vietnamese accomplished two important goals: they had gained valuable territory within South Vietnam from which to launch future offensives and they had obtained a better bargaining position at the peace negotiations being conducted in Paris.