The Veil

The Mainland exists on one of the prime material planes, but is partitioned from the outer planes by the Planar Veil (The Veil, The Celestial Veil, or one of its many other names). Magic has unimpeded access to the Elemental planes, as well as the demi- and quasi-elemental planes (The Ethereal, Astral, and demi-Shadow planes). Access to or from the Outer Planes is entirely blocked, at least for the most part. The last few decades have seen recent phenomena like Warlocks and other oddities.

The Veil also prevents most raise dead-type magic. While some powerful abilities which can revive the dead if applied quickly enough do still exist, no body dead more than 24 hours may be raised under any circumstances, not even by a wish or miracle spell. Additionally, no power that contacts the dead may be used on any corpse that has been dead for longer than 24 hours, up to and including wish and miracle.

While the Veil does prevent some direct summoning spells, especially of more powerful outsiders, many summoning spells for fiendish, fey, or celestial creatures are still allowed as many remnants of the these creatures remain trapped on this side of the Veil across the other listed planes or sometimes they can be pulled through weak spots between planes more easily.

A chaotic maelstrom at the furthest edges of the ethereal and astral planes. An absolute, two-way barrier between the material and material-adjacent planes and whatever lies Outside (or Beyond).