After the gold standard was abandoned at the outbreak of World War I and the Bretton Woods Conference following World War II, some countries sought exchange rate regimes to promote global economic stability, and hence their own prosperity. Countries usually peg their currency to a major convertible currency. "Hard pegs" are exchange rate regimes that demonstrate a stronger commitment to a fixed parity (i.e. currency boards) or relinquish control over their own currency (such as currency unions) while "soft pegs" are more flexible and floating exchange rate regimes. The collapse of "soft" pegs in Southeast Asia and Latin America in the late 1990s led to currency substitution becoming a serious policy issue.