Final answer:
Great Britain and France were the prominent nations that refused Hitler's demands on Poland, pledging to support Polish independence and declaring war on Germany after it invaded Poland.
Step-by-step explanation:
The prominent nation that refused Hitler's Polish demands was Great Britain. In March 1939, British Prime Minister Neville Chamberlain declared that Britain would support Polish independence. He announced that his government would assist Poland if its independence was threatened by German actions.
France joined Britain in pledging support to Poland, and by late May, an agreement was made for France to undertake air action against Germany should a war break out between Poland and Germany. However, despite these assurances, when Germany invaded Poland on September 1, 1939, Britain and France did not immediately provide effective military assistance but declared war on Germany two days later, on September 3, 1939. The Soviet Union, having signed the Nazi-Soviet Pact with Germany, also invaded Poland from the east, dividing the country between the two invading forces.