Bretton-Woods began to break down in the late 1960s. The Fed had been inflating the dollar more rapidly to help pay for rising federal expenditures such as those for the Vietnam war and Great Society programs. It collapsed altogether in August 1971. Here’s some material on Bretton-Woods:
http://mises.org/money/4s5.asp
http://mises.org/document/3967
http://mises.org/daily/3325
http://www.jstor.org/stable/30036415
