Since we just about passed the middle of summer, it would appropriate to talk about this cultural phenomenon. Midsummer is centered around the summer solstice and mainly observed in Europe. Many claim it was the religion before Christianity. Thus, when Christianity was founded and spread throughout Europe, Popes and the Church alike, found it much easier to incorporate Midsummer tradition into Christian beliefs rather than having them gone. The main observance during this cultural festival is the Great Feast observed on June 24 (6 months before before the birth of Christ).
As many of you may know, Midsummer or rather, "Midsommar" was a movie which came out recently. In this movie the tradition of Midsummer is only observed once every 90 years. Spoilers ahead if any of you have not seen this movie yet. Although the concept of Midsummer was based on the actual traditions, there were many things the movie took out of proportion. For example, there were examples of human sacrifice and narcotics.
The human sacrifice concept was centered around the belief of the seasons of life Midsummer observers believed in. Life begins in Spring and ends in Winter. When winter comes, it is believed that the person's life is over and instead of waiting for inevitable death, they offer their lives up in sacrifice. There is specifically 1 man and 1 woman who sacrificed their lives in the movie. It is not clear if it always has to be 1 elderly man and woman. However, what is clear is that the names of those who died are given to new born children, thus completing the cycle of life. To outsiders, this may be insane and incomprehensible, which is exactly what the main cast of the movie felt. I believe practitioners of "Midsommar" use this as a scare tactic to root out the weak and pick them off for their Great Feast sacrifice. This sacrifice involves 9 individuals for the 9 observed days of "Midsommar." Apparently the sacrifice is supposed to bless the people's crops and produce a bountiful amount of food.
You might be wondering how do these people obtain others for sacrifice and keep their population growing. Well, every now and then a person from the group is supposed to go out into the world and recruit potential candidates for sacrifice and reproduction. This is to also prevent inbreeding, but it does not mean they do not still participate in that. In fact, inbreeding is done every time the inbreeded individual dies. In the people's eyes an inbred individual has a clear mind and is unbothered by the natural occurrences of thoughts and emotion. The role of this individual is supposed to be an oracle of sorts. They are required to draw pictures and in return, the people of this religion are supposed to interpret what it means. Pretty sketchy if you ask me.
This cult-like religion has been operating for who knows how long, but one thing is for certain: they take advantage of the outside world and slowly and meticulously recruit individuals who fit their sacrificial needs and/or won't be missed.