If Japan attacks USSR turn 1, does that bring Germany and USSR into war?
If Japan attacks USA turn 1, and Germany/Italy did not attack the USSR turn 1, can USA land planes in USSR turn 1?
No, because the USSR is not at war with anyone.
Can only USA/USSR sea units share territory with all others when not yet at war? Or only with Axis or Allies? I assume land units may not share space.
Sea units may share a sea zone with anyone. Land units may not enter another power’s territory, and no other power’s land units may enter their territory.