The correct answer should be supplying the troops across a huge part of the globe
It was not possible for Germans and Japanese to connect forces because of the vast amount of land between them and the fact that they had to start fighting a defensive war, not an offensive one. It was difficult to supply everyone because for example, the British were fighting in both Europe and Africa, while the Americans were fighting in both Europe and the Pacific. This meant that people had to support both sides to prevent either from being lost.