One reason for the popularity of the euro in Finland is the memory of a 'great depression' which began in 1990, with Finland not regaining it competitiveness until approximately a decade later when Finland joined the single currency. Some American economists like Paul Krugman claim not to understand the benefits of a single currency and allege that poor economic performance is the result of membership of the single currency. These economists do not, however, advocate separate currencies for the states of the United States, many of which have quite disparate economies.