Short answers, pulled from the story.
Christianity has over 2.3 billion followers, around 28.8% of the world's population, making it the world's largest and most widespread religion. Its adherents form a majority in 120 countries and territories.
Christianity began in the 1st century in the Roman province of Judaea, after the death of Jesus, as a Judaic sect with Hellenistic influence. It originated as a Jewish movement within the context of late Second Temple Judaism.
According to Acts 11:26, the term "Christian," meaning "followers of Christ," was first used in the city of Antioch by its non-Jewish inhabitants. The earliest recorded use of the word "Christianity" was by Ignatius of Antioch around 100 AD.
Christians believe Jesus is the Son of God and the Messiah, both fully divine and fully human, who was crucified, died, and rose from the dead three days later. They hold that through belief in his death and resurrection, sinful humans can be reconciled to God and offered eternal life.
The three main branches of Christianity are Catholicism with 1.3 billion people, Protestantism with 800 million, and Eastern Orthodoxy with 300 million. Other prominent branches include Oriental Orthodoxy with 60 million and Restorationism with 35 million.
The Church of the East and Oriental Orthodoxy split over Christology during the 5th century, the Eastern Orthodox and Catholic churches separated in the East-West Schism in 1054, and Protestantism split from the Catholic Church during the 16th-century Reformation.
Emperor Constantine I decriminalized Christianity with the Edict of Milan in 313 and convened the Council of Nicaea in 325. On the 27th of February 380, the Edict of Thessalonica established Nicene Christianity as the state church of the Roman Empire.