DCA: north america
  DCB: south america
  ISP C: north american ISP
  ISP D: south american ISP

A major fiber link between north and south america is cut, disrupting all connectivity between the two areas.

  "lose the link between DCs A and B": check.
  "lose the link from ISP D to DC A.": check.

replace north and south america with any two disparate locations.