Archipelago fan here.
Controlling an island or a small continent is the best form or self defense being surrounded by water. If you can be very proactive early and establish contact with most of the world civilizations via map making it will give you a tremendous advantage. If you trade technologies with 16 civilizations you will almost ensure that your civilization maintains its standing as one of the most advanced; which is particularly helpful if you have a poor starting position.
Then when aiming for world dominance with an Archipelago map, you can take the world over one island at a time. The AI doesn't seem to fight back very well unless playing in a military alliance, whereby a combined arms approach morphs into a combined military approach presenting more trouble especially making your shipping lanes vulnerable. In a continent world map, the AI can invade you from several fronts easily with an alliance if on contiguous territory which makes it more dangerous.