Complex sentence: On 15 August 1971, the United States unilaterally terminated convertibility of the US dollar to gold, effectively bringing the Bretton Woods system to an end and rendering the dollar a fiat currency.
Split into simpler sentences: On 15 August 1971, the United States unilaterally terminated convertibility of the US dollar to gold. This brought the Bretton Woods system to an end and saw the dollar become fiat currency.