Which u. s policy decreased imports to the united states in the 1920s making it difficult for european nations to repay their war debts?

Tariffs--taxes were placed on imported goods in the US preventing many of those products from being sold. 

The 1920s tariffs were an effort to keep imported goods out and stimulate American businesses without European competition. Those businesses however were not able to sell their products and therefore could not pay taxes and lastly the governments were not able to pay back debts to the US from World War I. 

2cars an a racing track so the drivers can race