History: the origin of the Slavs is a much debated topic, though the most likely explanation is that the Slavs, who are descendants of an Indo-European tribe, settled somewhere between the rivers Don and Vistula where they mixed with Asian (Uralic) hunter/gatherers and nomadic people of Turkish and Iranian origin.
These nomadic people were mainly Scythians and Sarmatians who probably came from modern day Iran or central Asia, the word "Slav" is even believed to be derived from the old Iranian sacral word "Slovene".
The word "slave" is also derived from the Slavs; Germanic *Slawo meant both "Slav", "slave", and "dumb person", probably because many Slavs were sold as slaves during Germanic conquests in eastern Europe.
Another Germanic word for the Slavs was *Weneþaz, which was probably derived from Slavic "Wenetoi", a similar name ("Wenden") was later used for the Slavic tribe of the Sorbians, and in Estonia the Russians are still called "Wends".
The Slavs are believed to have originally lived in small matriarchal clans instead of large tribes like many Germanic and Celtic communities did.
However, from their small local communities the Slavs soon started to develop into larger and higher organized communities with mutual alliances, during their expansion they learned from the other peoples they encountered and took over many new inventions and cultural aspects.
During the Great Migrations the Slavs invaded eastern Germania that had become highly depopulated after wars and migrations and in the 6th century AD the Slavs even reached the rivers Elbe and Saale where further expansion was halted by powerful Germanic tribes like the Saxons, Vandals, and Thuringians, other Slavic tribes migrated to the south into the Balkans where they took large pieces of land from the Eastern Roman empire.
During the Middle Ages most of the lands between the rivers Elbe and Vistula including eastern Prussia (former "Gothiskandza") were retaken by the Teutonic knights of the German Order and most Slavic tribes were expelled from those areas, they were replaced by German farmers who cultivated the land and founded new cities like Elbing (Elblag) and Königsberg (Kaliningrad), only the Poles and some remnants of the tribe of the Sorbians stayed behind.
In World War II the Germans (the modern ones) were driven out of their eastern provinces again so these days the river Oder is the border between the Germanic and Slavic peoples.
In the Middle Ages most Slavic tribes were Christianized and formed countries like Poland, Russia, Bulgaria, and Serbia, especially Russia grew into a powerful empire that extended from Europe to the Pacific ocean; with its 145.000.000 inhabitants and 17.000.000 square kilometers of land it is now the biggest country in the world.
Culture: there are 3 cultural groups of Slavs; West, East, and South:
Western Slavs: Poles, Cashubians, some remnants of the Sorbians in the German area of Lausitz, Czechians, and Slovakians.
Eastern Slavs: Russians, Ukrainians, and Belorussians.
Southern Slavs: Slovenians, Croatians, Serbians, and Bulgarians.
The Elbe-Slavs (Abodritians, Veletians, and Sorbians (also called Wenden)) belonged to the Western group but are now extinct.
Nowadays the Western Slavs and the Slovenians and Croatians are mainly Catholic and use an adapted Latin alphabeth, the rest of the Slavic peoples are Eastern Orthodox Christians and use their own alphabeth; the Cyrillitsa (Cyrillic).
Language: just like the Slavic culture the Slavic language can be divided into a Western, Eastern, and Southern group, to give you an impression of those languages I shall now give three examples of Slavic languages, the first one is Polish, a western Slavic language, the second one is Russian, an eastern Slavic language, and the third one is Serbian, a southern Slavic language:
(Universal Declaration of Human Rights article 1)
"All human beings are born free and equal in dignity and rights.
They are endowed with reason and conscience and should act towards one another in a spirit of brotherhood."
Some snippets of information about the Slavic religion are known to us from historical writers but most of it would have been lost forever without the work of Alexander Afanasjev (1826-1871), who collected Slavic folklore and fairy tales like a modern Snorri Sturluson and saved many remnants of the old Slavic traditions.
Afanasjev published 8 books full of Slavic folklore and 640 legends that were well received by the people, the church saw this sudden interest in the old Slavic traditions as a threat so the second edition of Afanasjev's myths was burned, but the renewed interest in the Slavic traditions could not be reversed.
The ancient Slavs believed in House-spirits (Domovoj), Forest-spirits (Lesjii), and Water-spirits or Mermaids (Rusalka), they also knew witches, magicians, werewolves, (like the wolfman Vlkodlak) and vampires.
Especially the vampire (South Slavic: "Vampir") is a specific Slavic belief that was especially strong on the Balkans, even today there are people there who still believe in these beings.
The fear of vampires was even further ignited by the church, which claimed that all heathens, witches, magicians, thieves, and prostitutes would come back as vampires after death to visit people at midnight to drink their blood or have sex with them, after this the victim died or became a vampire himself.
When Bram Stoker heard about these myths he combined them with the historical character Vlad Tepes and some of his own inventions to create his work "Dracula".
A good example of a witch is Baba Yaga (or Jezi Baba), who is an evil old woman who eats humans, she is half human/half tree and she wears a beard, she also lives in a dancing house on chicken-legs that is surrounded by a fence of human bones and to move herself she rolls over the ground or flies around in an iron cauldron.
The Slavs also worshipped wooden idols of their gods who often had multiple heads that symbolized wisdom and omnipresence, this idols mostly stood on a hill or in a sacred forest, the Slavs did not have many temples and only the Sorbians knew temples and priests, but unfortunately most of those have been destroyed during the Christianization, the same goes for the wooden idols of their gods.
Description of the main Slavic gods:
Triglav ("three-heads") is a three-headed wargod, the Slavs had constructed 4 temples for him near Szczecin (Stettin) where they offered 10% of their spoils of war to him, they also kept a holy black horse in the temple, during the Christianization the temples and statues of Triglav were destroyed and his three heads were sent to the pope in Rome.
Svarazic / Svarozic / Svarogich is the god of fire and he was believed to have created the sun, human sacrifices were also made to him like for instance the bisshop of Mecklenburg who was sacrificed to him in 1066.
Veles / Volos is a fertility god and the patron of herds and shepherds, in 988AD king Vladimir of Kiev ordered an idol of Veles to be thrown in the Dnjepr but he remained so popular among the Slavs that the church decided to equal him to st.Blasius, even until the 19th century Veles was worshipped by farmers.
Dazhbog (Serbian: Dabog / Polish: Dazbog) is the sungod and he is reborn every morning, during the day he rides in his diamond wagon (the sun) through the sky, at the end of the day he has turned into an old man and dies when it gets dark, the next day he is reborn again.
Dazhbog is the son of the Skygod Svarog and the brother of the firegod Svarazic, he is married to Myesyats (godess of the moon) and the Slavs believed that their matrimonial disputes causes earthquakes.
Myesyats is the godess of the moon, she is married to Dazhbog (the sun) and their children are the stars, in Autumn they always divorce but they will remarry in Spring.
Mati Syra Zemlya ("Mother Moist Earth") is the Slavic earthgodess, the Slavs worshipped her during harvest time; at dawn they sprinkled hemp-oil over their fields and called upon her while bowing down to the directions of the four quarters (north, east, south, west) while sprinkling oil.
Perunu (Russian: Pyerun / Polish: Piorun, Perun) is the thundergod, until the 10th century there was an idol of him in Kiev with a silver head and a golden moustache.
Perunu is believed to have originally been a god of agriculture who was later turned into a god of thunder due to Indo-European influences, this also explains the similarities between Perunu and other Indo-European thundergods, some of his similarities with the Germanic god Thunar (or Donar/Thor) were probably adopted later from the Vikings that invaded the area around Kiev.
Perunu is also a god of rain and during times of drought the Slavs performed a ritual to ask him for rain; a chaste girl who was naked and decorated with flowers danced around in a magical circle while being intoxicated with alcohol or drugs.
The people also sacrificed livestock to him and he was believed to fly through the air on a millstone while throwing lighting bolts to the earth, several towns have also been named after him like for instance Perunji Ort in Slovenia, Peruna Dubrava in Croatia, Perin Planina in Bulgaria, and Peruny and Piorunow in Poland.
Perunu's worship was ended by king Vladimir of Kiev who converted himself to Eastern Orthodox Christianity, because Perunu was so popular among the Slavs king Vladimir decided to equal him to the holy Elia.
Svantovit / Svantevit is a god of war, on the German island of Rügen the Slavs constructed a temple for him with a 10 meter (around 32 feet) high idol of him with four heads, they also held a holy white horse in the temple on which the god was believed to ride at night, the outcome of a war or battle could also be predicted by looking at the horse's behaviour, in 1169 the Slavs on the island of Rügen were defeated by the Danish king Waldemar and the temple of Svantovit was destroyed.
Ancient Slavic holidays:
January 1: Offering to Svantovit for prosperity during the upcoming year.
March 21: Celebration of the Spring Equinox and the beginning of Spring, this fertility festival was dedicated to Perunu though Mati Syra Zemlya and her husband Yarilo (god of love and agriculture) were also worshipped during this time.
June 21: Celebration of the Summer Solstice and the beginning of Summer, the re-marriage of Dazhbog and Myesyats was also celebrated.
June 24: Festival of Mati Syra Zemlya.
August 1: Offering to Mati Syra Zemlya.
September 22: Autumn Equinox and the end of summer, on this day the Slavs mourned the death of Yarilo, who was a god of harvest who died at the end of the harvest period and was reborn when the next one started.
December 21: Winter Solstice and the beginning of Winter, on this day the Slavs mourned the divorce of Myesyats (moon) and Dazhbog (sun) and held a festival for Stribog (god of the winds).