During the fifth Fuyuki Grail War, a mysterious outside party found their way to the Holy Grail during the proceedings and made a disastrous wish upon the corrupted chalice - "I Wish For More Wishes". With the unfilled power of the Grail incapable of fulfilling this desire directly, it broke into untold pieces, creating shards of the Holy Grail that scattered across the worlds which then began gathering magical power directly from the land and the people that lived where it landed.
Each Fragment of the corrupted grail's power varies on size and power, but each is capable of granting one wish whose power varies wildly from the mundane to the fantastical. Untold numbers of "Grail Wars" have broken out, and Servants - sometimes the same Servant, sometimes the same Servant appearing simultaneously in a strange Class Container - have begun appearing at random to masters both suitable and unsuitable.
The Mage's Association, lacking a better term for the event (and incapable of numbering the Grail Wars at this point), has dubbed it the "Grand Grail Crisis" and has enlisted the aid of the Church to suppress the Grail fragments as they pop up and stop people from making dangerous wishes upon the fragmentary chalice, for what good it does. Others use the event for personal gain or to carve out fiefdoms with newfound power, for amusement and sport, or frivolous fun.
(Note!: This Fate theme is based loosely on Fate/Grand Order and treats the standard rules of the Nasuverse as guidelines at best, and should be considered wildly non-canon. It will probably break rules of the canon Nasuverse pretty regularly. Please contact Elizabeth for information.)