It's not that silly of a question!
Until the mid-'70's, the USA was divided into two sections, which could NOT exchange power. All PoCo gennys were "synchonised" with others in their respective grids- but somewhere (in Nebraske, I believe), the "western" grid met the "eastern" one....and they were just far enough out of sync to make interconnection impossible.
Now, I do not recall the specific details, but I recall quite a fuss was made over some chap who found a way to interconnect the grids. I seem to recall him getting some fancy prize for his efforts. I believe the two grids are still out of sync, but they are able to feed each other.
