Ancient Greece at the height of its power vs Greece of today.

Not a historian but I assume the time of Alexander or similar is Ancient Greece's strongest.

Situation 1: Both Greece's are transplanted from earth to be islands around 1 mile apart. No other land.

Situation 2: A mile-wide portal between old and new Greece opens just outside Athens. For some reason, all people and nations outside the borders of Greece refuse to acknowledge or participate in the war.

Situation 3: Same as 2, but other nations and people have full power to get involved if they choose.