Civilization III: Conquests is the eagerly awaited expansion pack for Civilization III, and expand the game it certainly does.
Conquests includes all of the material in the Play the World expansion except for a few user-created scenarios now available as free downloads from the developer's website.
In short, if you buy Conquests, you don't need Play the World but you still need the original Civilization III game.
The Conquests expansion includes nine professionally and lovingly created conquest-themed scenarios. Each scenario is so detailed it could almost be a separate game but, being greedy, I would have liked even more of them.
Far from being simple scenarios, tech trees, units and even the in-game Civilpedia have been changed in each to give more flavour.