Monarch sent you this? What's all this malarky about 'more than one carrier', they don't interline. And as they are not a US carrier they have no traffic rights for 'domestic travel wholly between US points'.
Something funny here, it looks like they copied a US carriers CoC word for word. I'm beginning to doubt their professionalism.
If that is the case, then their
professionalism is far superior to your ability to
Google! Because if you did, you would quickly discover that the wording is a set down part of the ICAO Montreal convention text. More formally, The Convention for the Unification of Certain Rules for International Carriage by Air.
All airlines use it.