The First World War marked a decisive change in the way that the peoples of Europe and North America understood their world. There was the pre-war world, the First World War, and the post-war world. Formerly, families were whole, communities were often prosperous, and optimism for the new century was widespread. The First World War changed all that. In people's memories, the past seemed still brighter; the future, more worrisome. The conflict also decisively changed the way the world's economic and political systems worked.
Britain's economic supremacy was gone. Now, the United States and Japan were the world's major industrial and trading nations, while Russia, thanks to the revolution, was excluded from world markets. For many years the economies of the major European combatants would suffer from war damage and war debts. The latter were largely owed to the United States and paid out of German reparation payments. Internationally, governments raised tariff barriers to protect their domestic markets.