General Networking Question

in CCIE
How are routers set up when you have dozens (if not hundreds) of networks, thousands of branches, and offices all over the world (all for one corp)?
I used to work for a VERY large bank, and based on my CCNA studies so far, it seems like that kinda setup would be a monster...
I used to work for a VERY large bank, and based on my CCNA studies so far, it seems like that kinda setup would be a monster...