Global Prosperity

The four end-game technologies can be researched in any order. Each of them costs a great deal, and the cost in Knowledge increases with each that you research. The cost hikes are predictable, and by this point in the game you will produce as quickly as any resource, if not more so, and probably be at the cap.

Settling on the order in which to research these technologies can have a profound effect on combat, and even the outcome of the game.

The time it takes to research these technologies is greater than any other; you can crush (or lose) an entire army waiting for the work to be done. Enter the Information Age rich, and you can research them simultaneously if you build multiple Libraries (one per city).

Global Prosperity raises the efficiency cap for all your resources to the absolute maximum, no matter where they had been at the start of the research. Deploy enough Citizens (and build enough gather buildings) and you can fuel an enormous war machine with the proceeds.