Civilization – Any way to play an “original” game of Civ 5

If you have up to date video drivers, then the most likely cause is a bad civ 5 install or bad Steam data on Civ5. I've had this sort of issue with Steam before, just not on Civ5 specifically.

• First order: make sure you have latest drivers.
• Second order: Verify integrity of Civ 5 installation via "Verify Integriy of Game Cache".
• Third order: delete Civ 5 off the box, reinstall from Steam.
• Fourth order: copy SteamApps data to temp space, delete steam, reinstall steam, copy SteamApps data back.

That's all the steps I've had to take in the past to get a broken steam game working. If none of this works for you, sorry, but this list has been all I've ever had to perform. Although I have had to do the first and second options repeatedly to fix a game.

Yes, you can pledge to protect City-States without the Gods & Kings expansion. The mechanic changed for the expansion however, now allowing you to pledge to protect city states immediately, while before it required you to at least be friends with the city state before you are allowed to. For some reason, the AI is still allowed to pledge city states right away, even in the base game. G&K just evened the playing field in this sense, but you won't need to buy the expansion to use the mechanic.