The Pact and the Silence are, roughly speaking, two sides of the same agreement. The Pact is the agreement itself, worked out between the Fatae and Richard III (and his advisors) in 1483. (Read about
The Silence for more details on the mechanics there.)
Learn more about the historical reasons
In 1483, Edward IV died. His younger brother, now Richard III, realised that his nephews (children of Edward V and Elizabeth Woodville) did not have the magical ability to hold the
land magic in the way a King - or the King's close representative - needed to be able to do.
(I have some theories about why this happened, and need to do some more background research to confirm the way I want to handle this, so the details are as yet unspecified.)
In the course of the next fifteen months, he and a number of others arranged a ritual in November 1484, with six planets in Scorpio (including Jupiter and Saturn, which is what makes it a Great Conjunction). If you follow astrological magic theory, and you want to completely rework your country's civil and magical structures, that is a great time to do that ritual.
The result was the splitting of the magical and non-magical communities, the creation of the Council to take the King's place with the land magics, and all the details that fall out from that.
The Pact is, actually, a relatively beneficial agreement to both sides.
The humans agreed to allow the Fatae spaces that they would not be bothered or encroached on (mostly places not very suitable for human habitation), and to avoid interfering with Fatae magic in specific ways. (Many of these have come down through folklore in various ways.) This leaves the Fatae relatively free to see to what they see as their magical obligations - places where there is a thinness between the worlds or planes of existence, places that magic is particularly wild and complex, places that need additional protection.
There are some mystical initiatory societies that seek out the mysteries of different kinds of Good Folk, which are buried in allusionary poetry.
In turn, the Fatae provided access to specific magical skills and implementation (most notably the
portals, but also various forms of
warding and protective magic, and some specific techinques for healing, alchemy, and other complex magical needs.) They also agreed not to unduly tempt or harm humans outside of certain clearly specified agreed terms.
The Council, of course, is the interface that deals with things no one thought to make an agreement about, or when the existing agreements are clearly inadequate.
The Pact and the Silence are focused. They apply to Great Britain (England, Wales, and since 1707, Scotland, though effective agreements similar to the Pact were in place before that in Scotland.) It notably does not include Ireland, no matter what the non-magical politics would like to tell you. The Irish magical community makes their own arrangements.
However, thanks to the Empire, people in the British Empire who come up through the British educational system or contacts abroad (and certainly the children of Colonial Service and Army magical folk stationed through the Empire) make the Pact, as do a number of others whose lives bring them into close contact with the British Empire.
(
Rathna and
Gabe speculate about this in the epilogue of
The Fossil Door. There will be more coming exploring this in the future.)
Similarly, the United States, Canada, Australia, and New Zealand all function under similar agreements to the Pact (even though there are other things going on with the local magic in those places.) Also, notably, the
Land magic expectations work very differently outside of Albion proper.
Basically, if you assume that colonialism provides an overlay outside of Albion proper, and a lot of that is a purely social agreement and convention that most people go along with because it's what they're accustomed to (or because those rules and agreements do apply to them back home), you're in the right place. Your assumptions may, however, come back to bite you at an unexpected moment.
