A war without American combat entry depends on Japan staying out

What might have happened in World War II without American help?

Britain and the Soviet Union could probably continue if US supplies still flowed and Japan stayed out, but the war would take longer; removing American industry as well makes the result far less certain.

American combat participation and American industrial supplies are separate questions. If US supply continued and Japan stayed out of the war, the British Empire could probably still win in North Africa while Soviet forces fought on in the east. German conquest of Britain remains unlikely in this assessment, though the Mediterranean campaign and other operations would probably take longer. Shipyards in Canada, Australia, and India would gradually add resources, and the empire had further manpower available, including the Indian Army. Withdrawing American supply as well makes the outcome harder to judge. Sending British troops to serve alongside the Soviet army had also been considered, but incompatible approaches to force discipline were judged an obstacle.