Do we make campaigns for the other countries besides US
and use the same campaign number?
Yes, initially, I created Campaigns, for almost all of my sites, but after Jorge's suggestion, i started just use the default ID, easier to remember just one number, and use a unique custom ID, usually the sites name. To my understanding, the IDs are mainly for tracking, so you can see which sites are performing the best.
or what do the new campaigns point to?
I do not understand this question..

After you watch the video and maybe EBay's tutorial, it might be a little clearer than I can explain here.

For me it is just easier not to have to worry about trying to remember all of the IDs and just customize the custom Id.. Hope this helps.