The cities of Leningrad, Moscow, and Stalingrad lay on the border

During World War II, the Soviet Union was an Allied nation, while Germany and its partners were Axis nations. German forces advanced into the Soviet Union and threatened Leningrad, Moscow, and Stalingrad, placing these cities near the boundary between Allied and Axis-controlled territory. So the best choice is “between Allied and Axis nations.”

AI-written and checked against the verified answer.