War with the Soviets could align Scandinavia with Britain

How might Finland and Scandinavia react if Britain fought the Soviet Union as well as Germany in 1939?

Finland would probably align with Britain, Sweden would often follow, and Norway could join them, making Germany's already risky Norwegian operation far harder.

A British declaration of war on the Soviet Union could draw Finland toward Britain and make Swedish support likely. Norway would then face a stronger incentive to join because both Norway and Sweden feared Soviet expansion through Finland. Allied preparation could mean armed forts, British minefields, and Royal Navy access to Norwegian ports before Germany moved. Since the historical German invasion already depended on a narrow margin, those changes could make the Norwegian campaign fail or prevent it from unfolding in the same form.