Image: September 1, 1939 Los Angeles Times newspaper front page.
This act of war marked the beginning of what was later called World War II.
“By the start of the Great Depression in 1929, America was mostly unarmed and determined never to get involved in European feuding again. Most Americans complained that the huge death toll of World War I had led to neither perpetual peace nor even a peaceful Germany.
“America’s isolationism and disarmament also helped prompt another global war. Had the U.S. kept its military strong after World War I, and had it entered into a formal alliance with its former World War I partners, Germany never would have risked a second war against the combined strength of a fully armed Britain, France and United States.
“Instead, Hitler assumed the U.S. either could not or would not offer much military help to his intended European targets.”
Excerpt from an editorial comparing events then to those today: http://www.investors.com/politics/on-the-right/appeasement-collaboration-isolationism-its-looking-like-europe-39/ . The excerpt and link is to an opinion piece and does not necessarily reflect the opinion of this blogger. It provides a concise description of the situation. There is no shortage of opinions from scholars, politicians and many, many others about the influence of events before the invasion of Poland.
Although the United States did not officially declare war until Dec. 11, 1941 it assisted in supplying war materiél to Allies in Europe before then. Manufacturers in southern California were instrumental in building aircraft and myriad other products. That resulted in significant economic and other changes beginning in the late 1930s..