As opposed to the previous Civs, you cannot or should not aim at occupying all cities on the planet; corruption and reconstructing the infrastructure makes it unworthy. However, as the winner is always relative to the other participants, dispatching smaller “punishment expeditions” do work if you are about to maim, hinder and set back an opposing civilization. This includes:
- Destroying their roads to resources
- Burning down their city improvements
- Killing population
- Stopping their shipping to prevent expansion.
All the above can be done by a generally isolationist state, by sending out contingents of 2-3 ships, one transporting artillery pieces and defenders (Artillery and Infantry is the best choice) and the rest escorting the transport.
Upon arrival, you unload the saboteurs onto a hill or mountain (to provide better defense and a prolonged stay) near the target area, which should be a resource site, a traffic node or some large cities. If lucky, your artillery can fire at 3-4 targets of your choice. You can take a worker too, he will build a fortress if needed. Then you start pounding the improvements, then the cities, and any approaching enemy unit. If you have a faster unit at hand, you can even capture workers; transport them home with the vessel if you want.
Meanwhile, the gunships will visit some coastal cities and bombard; they can also kill transport vessels to do more economic damage.
I have tried this strategy against large and distant empires. Although I cannot be sure about the economic balance, I guess the vast damage was worth the 2 Infantry and 2 Artillery: they “leveled” 2 cities of size 11, blocked their Iron source and defended against countless attacking units.
As I did not need their cities, that was more than enough to cripple a rival and ensure my triumph.