Question

Which u.s policy decreased imports to the United States in the 1920 making it difficult for European nations to repay their war debts

Answer 1

Tariffs on imports

The 1920s presidents began a system of tariffs on imported good to encourage spending on American goods only. However, with no trade, European countries were unable to make money. 

Tariffs are taxes on imported goods. This is a common economic policy of conservatives.