The talks faced a number of obstacles. The Russian State Duma's refusal to ratify the START II treaty delayed the start of formal negotiations by more than two years after Yeltsin and Clinton completed the initial framework discussions in 1997. Ratification had been delayed because of Russia's opposition to Operation Infinite Reach, the NATO bombing of Serbia, eastward expansion of NATO, and America's plans to build a limited missile defense system (which would have required changes to or the US withdrawal from the 1972 Anti-Ballistic Missile Treaty).