Overall, in Civ3 land is king. More land means more resources, more space for cities, more tiles to be worked that produce commerce. Commerce is filtered thru the sliders to become science, gold, and happy faces.
Many experienced players recommend warring when you have an advantage, especially after completing a key tech to enable your military like Military Tradition for cavalry. On many maps, it is easier to conquer the territory where the resources are, rather than trading for them.
At the same time, selling your excess luxuries for gold-per-turn will slow down the AI's economies and tech speed, while giving you excess gold for rush-buying units for a future war.
Many experienced players recommend warring when you have an advantage, especially after completing a key tech to enable your military like Military Tradition for cavalry. On many maps, it is easier to conquer the territory where the resources are, rather than trading for them.
At the same time, selling your excess luxuries for gold-per-turn will slow down the AI's economies and tech speed, while giving you excess gold for rush-buying units for a future war.