What did the US fear might happen if Japan's economy remained weak after WWII? *

US feared retrenchment and dull nature of Japanese economy after ww1

Explanation:

The US feared that The Japanese economy will suffer from a retrenchment after the boom of the First World War. For most of the decade, the real economy remained dull, with low economic growth, mild deflation, and an unsettled financial system.

Toward the end of the war, Japan increasingly filled orders for needed war material for its European allies. The wartime boom helped to diversify the country's industry, increase its exports, and transform Japan from a debtor to a creditor nation for the first time. Exports quadrupled from 1913 to 1918.