What reinforced isolationist sentiments against U.S. involvement in World War II?
World War 1 & Economics
After the human cost of WW1 there was popular support for US disengagement from world events, even though Woodrow Wilson had been the driving force behind the creation of the League and Nations he could not persuade congress to allow US membership through the fear of the US being dragged into another ruinous war
The depression of the 1920's drove down wages and the US closed its doors to immigration, this could be sustained as by and large the great projects of the previous 50 years were complete (the railways) and there was no need for mass low skilled labour
In an effort to restart the economy trade barriers were set up against imported goods which further isolated the US
There were also various socio-economic theories that saw non whites as less than equal which fueled anti immigrant policies
There were also frictions with relationships with foreign countries due to war debts, Britain had lent vast amounts of money to Russia, France and Italy to fund their war efforts, but later on in the war was forced to borrow from the US to sustain its own war effort - Russia defaulted on the loans due to the revolution and France and Italy were incredibly slow in repaying any debts but the US was pressing Britain for repayment