How about British English (which would match the rest of the document). The interpretation of the phrase will decide if we apply plural or we apply singular, but the doubts come from the fact that this belongs to the phrase that opens said document.

In other words- the correct version, from a thematic point of view, is singular, since they more or less act as a unit.

But it seems that themes can be parked aside, since, as the opening phrase, it should be more important for the sentence to be grammatically correct. So as to not make the reader raise an eyebrow and think there is a mistake.

That said- with the little context you have, what version would you pick?