The decline and collapse of the Soviet Union and the disappearance of the Red Army meant that there was no longer any military constraint on the United States.

NPR: Author Kinzer Charts 'Century of Regime Change'

"If the United States is ever called upon to fight deep in east central Europe against the Red Army or the Russian armies, this country will be divided far more deeply than it was during Vietnam, " former presidential candidate Pat Buchanan said.

CNN: AllPolitics - Big Issues Confront NATO At Madrid Summit