Jim Mokhiber was an Associate Producer on FRONTLINE's documentary "War in Europe."

Many in the diplomatic community and beyond suggest that Milosevic's decision to withdraw his troops from Kosovo stemmed from his continuing inability to divide the NATO allies. During the war, the alliance weathered disagreements over strategy and embarrassing -- sometimes tragic -- targeting mistakes. In late April, organizers toned down celebrations scheduled for NATO's Fiftieth Anniversary summit in Washington. While behind-the-scenes squabbling continued, by the end of the summit the allies had agreed to intensify the war they could not afford to lose. From then on, even major wartime errors, such as the bombing of the Chinese embassy on May 7, failed to break NATO solidarity.

Late in the war, Serbia's diplomatic isolation mounted as Russia began to cooperate with the NATO allies and abandon its blustery support for its fellow Slavs. The change was dramatic. At the beginning of the war, Russian Prime Minister Yevgeny Primakov had turned his Washington-bound plane around in mid-flight to signal his country's displeasure. Weeks of anti-NATO popular protest and official posturing ensued in Russia. However on April 14, 1999, Russian President Boris Yeltsin appointed Viktor Chernomyrdin as his chief Balkans envoy, signaling Russia's desire to chart a new Kosovo policy and to salvage its essential relationship with the West. After a series of marathon negotiations with U.S. Deputy Secretary of State Strobe Talbott, Chernomyrdin and Finnish President Martti Ahtisaari successfully presented NATO's demands to Milosevic in Belgrade on June 3.

Air power advocates, including Lt. Gen. Michael Short, stress NATO's decision to "go downtown" and attack strategic targets in Serbia and central Belgrade. In contrast to NATO's Supreme Commander Wesley Clark, Short has criticized "tank plinking" in Kosovo as wasted effort, comparable to the meaningless "body counts" of the Vietnam War. Pilots, he contends, could not stop ethnic cleansing on the ground below, and damage to Serbia'sThird Army in Kosovo did not resonate with policymakers in Serbia proper. Only when NATO sought to "go after the head of the snake," Short maintains, did the implications of the war in Kosovo start to become clear to Milosevic and average Serbs. Throughout the conflict however, political leaders in the NATO alliance sought to rein in their military commanders, particularly after the disastrous May 7 bombing of the Chinese embassy. But by the end of May, NATO bombers had won approval to strike hard at Serbia's infrastructure, including its central power grid.

On March 24, 1999, while NATO prepared its bombers, President Clinton announced that the United States would not send ground troops to fight in the Balkans. As the air war dragged on with uncertain results, critics and allies alike began to question the wisdom of the President's declaration and position. In early May, NATO officials quietly began exploring ground invasion options, and by the middle of May, the President was publicly noting that "no options are off the table." The allies also began to reinforce key roads and bolster forces deployed in Macedonia and Albania. After Milosevic folded on June 3, administration officials let it be known that the President had been on the brink of deciding whether to mobilize for a potential ground war -- the implication being that the regime in Belgrade had just missed a NATO bullet. How close the U.S. and NATO really were to such a deployment -- and the almost certain casualties, political costs and diplomatic schisms such an invasion would have entailed -- is uncertain. In the end, however, the threat may have been real enough to push Milosevic to accept NATO's demands.

Some observers contend that a resurgence of the Kosovo Liberation Army (KLA) in the latter phase of the war sharply increased the effectiveness of NATO bombing. As military analyst Anthony Cordesman notes, the KLA increasingly provided NATO with targeting information and flushed Serb troops from their dispersed hiding places. For example, some have pointed to NATO's B-52 bomber strike in early June against a concentration of Serb troops battling the KLA on Mount Pastrik. Immediately afterward, allied military officials suggested to reporters that the strikes had resulted in massive Serb casualties and may have helped speed Serbia's withdrawal. Since the end of the conflict, however, many analysts have challenged this assessment, noting that the Mount Pastrik site offers little evidence of such extensive damage. (Indeed, several analysts claim that it was the clearing of the Balkans' poor weather, and not the KLA offensive, that increased the effectiveness of NATO's bombs.) Nevertheless, NATO's demonstrated willingness to work in conjunction with the KLA - despite U.S. officials' early assurances that the alliance would never become "the KLA's air force" - may have unnerved Belgrade.

A minor but mysterious role may have been played by a campaign to increase pressure on Milosevic's associates and family, including his influential wife Mirjana Markovic. According to some reports, this secret effort - allegedly dubbed "Operation Matrix" and run by diplomat and Balkans expert Robert S. Gelbard - squeezed the Serbian power elite by limiting their ability to leave the country and targeting their factories and other assets. On Nov. 8, the WashingtonPost.com's military affairs columnist William Arkin suggested that CIA "Matrix" planners were seeking to bomb a Serbian ministry with ties to Milosevic's cronies when they mistakenly targeted the Chinese Embassy on May 7. While NATO Supreme Commander Gen. Wesley Clark denies any knowledge of "Operation Matrix," the Pentagon recently admitted employing psychological and economic tactics that "raised the level of anxiety and discontent within Belgrade's power circles."

Former National Security Advisor Zbigniew Brzenzinski suggests that Serbia withdrew from Kosovo only after Russia made a secret deal with Milosevic -- a "desperate double-cross" of NATO that would impose a de facto partitioning of Kosovo into Serbian and Albanian spheres. According to Brzezinski, the plan was hatched in late May and early June, at the supposed height of Russian-NATO cooperation. On June 10 and 11, as NATO planned its entrance into Kosovo, two hundred Russian soldiers dashed from their base in Bosnia, through Serbia and into Kosovo, where they took up positions vacated by the departing Serbs at the Pristina airport. Shocked NATO commanders, including NATO Supreme Commander Wesley Clark and British Lt. Gen. Michael Jackson, immediately began arguing about appropriate responses. In a phrase later made famous, Jackson reportedly refused Clark's order for a vigorous military riposte, saying "I won't start World War III for you." In the end, Brzezinski writes, the Serbo-Russian gambit failed when Hungary, Bulgaria and Romania refused to allow Russia to use their airspace to fly in reinforcements. Their hand weakened, the Russians ultimately accepted NATO's refusal to give them their own distinct peacekeeping sector in post-war Kosovo.

On May 24, 1999, Serb President Slobodan Milosevic became the first sitting head of state to be charged with war crimes in the midst of an armed conflict. Along with four other high-ranking Serbian leaders, Milosevic was accused of offenses including murder, deportation and persecution in Kosovo. After the International Criminal Tribunal for the Former Yugoslavia (ICTY) announced the indictment on May 27, many worried it would complicate the search for a settlement. Prosecutor Judge Louise Arbour admitted as much when she stated that the indictment raised "serious questions about [Milosevic and his deputies's] suitability to be the guarantors of any deal, let alone a peace agreement." Nevertheless, the following week, mediators representing the G-8 returned to Belgrade to continue their ultimately successful meetings with Milosevic. Since the end of the war, some, including former British Secretary of Defense George Robertson, have credited the indictment with adding to the international pressure that led Milosevic to capitulate.