Basic Timeline:
-Phtumeran civilization flourishes after making contact with Great One Ebreitas. Blood ministration discovered, civilization collapses in the wake of the birth of the new Great One Mergo, sired by Queen Yharnam (white dress lady). Great Ones cannot birth their own Children, a surrogate must be chosen.
-City of Yharnam begins, built over top of Pthumeran civilization. Scholars at the college of Byrgenwerth (Willem, Laurence, Gherman, Rom) delve deep into the ruins, searching for secrets of the race. They make first contact with Ebreitas, who teaches them blood ministration.
-Willem and the others attempt to beseech the Great Ones for power and insight. Rom is transformed into an immature Great One, but Willem is unsatisfied with the results.
-Laurence and Gherman split from Byrgenwerth and found The Healing Church, dedicated to studying and administering blood ministration. It's discovered to basically be a panacea and The Church, and Yharnam, flourish. It's not without side effects. The Plague of Beasts is discovered and The Hunt is founded. At this point the Church has split into 3 groups: The Doctors, The Hunters (led by Gherman) and the Choir. They are dedicated to blood ministration study, the Hunt, and the study of the cosmos/Great Ones respectively. A secret society known as Mensis grows within the ranks of the Choir, dedicated to summoning or creating their own Great One.
-The Hunts begin to grow worse and worse as the plague spreads, culminating in the first Blood Moon. Blood Moons are the time when circumstances are correct for a Great One to be born, and causes a violent reaction in the Blood resulting in a greater number of Beasts. The situation grows so dire that The Church quarantined Old Yharnam, and burnt it to the ground to stop the Beasts. Gherman's wife/daughter dies, having been chosen as a Great One surrogate mother, and his grief is absolute. He goes mad, constructing the doll, and is enraptured in the Nightmare by a Great One called The Moon Presence.
-Willem uses Vacuous Rom, now grown but no more useful to him, to seal the Blood Moon and the boundary between Nightmare and Yharnam. He then tries one last ditch effort to gain insight by putting eyes on his brain. Whatever that entails, it doesn't work, and Willem is left a gibbering wreck while the school continues without him.
-Byrgenworth scholars continue with increasingly dangerous and foolhardy attempts to commune with Great Ones. Byrgenworth ends up summoning Great One Amygdala, in the process losing their lecture hall to Nightmare. The Church seals the path to the now abandoned school and forbids entry.
-Mensis begins blood sacrifice rituals to prepare to summon a Great One.
-You arrive in Yharnam, and receive blood ministration. The Hunt begins again.