The Federal Reserve shifted its stance in the mid-1960s away from monetary orthodoxy in response to the growing influence of Keynesian economics in the Kennedy and Johnson administrations, with its emphasis on the primary objective of full employment and the belief that the Fed could manage the Phillips Curve trade-off between inflation and unemployment (Meltzer 2010).
Increasing US monetary growth led to rising inflation, which spread to the rest of the world through growing US balance of payments deficits. This led to growing balance of payments surpluses in Germany and other countries. The German monetary authorities (and other surplus countries) attempted to sterilise the inflows but were eventually unsuccessful, leading to growing inflationary pressure (Darby et al. 1983).
After the devaluation of sterling in November 1967, pressure mounted against the dollar via the London gold market. In the face of this pressure, the Gold Pool was disbanded on 17 March 1968 and a two-tier arrangement put in its place. In the following three years, the US put considerable pressure on other monetary authorities to refrain from converting their dollars into gold.
The decision to suspend gold convertibility by President Richard Nixon on 15 August 1971 was triggered by French and British intentions to convert dollars into gold in early August. The US decision to suspend gold convertibility ended a key aspect of the Bretton Woods system. The remaining part of the System, the adjustable peg disappeared by March 1973.
The problem that made the Bretton Woods system unsustainable was the fiscal expansion caused by the US having to pay for the Vietnam War and the Great Society programs. From the linked article: