Brief overview of history (my view)
James S. Trimm has a nice overview in his blog, How the Church Fathers Invented Christianity of the influence by Ignatius in the late first century. The beginning of subtle changes from Turah-based teachings. Simcha Jacobovici investigated Selling Christianity (2019, 44 min) about the birth of Christianity.
In 321 CE, the Roman Emperor, Constantine the Great, declared sunday to be the day of rest throughout the whole empire; this was in honor of the sun. With the support of Eusebius of Nicomedia he convened the First Council of Nicaea (wikipedia) in 325 CE to formally establish Christianity with the day of worship on sunday, when to celebrate Easter (the Christian Passover), and 20 other canons (or church laws). Per the wikipedia, it was meant to unify practices by the whole church and "forms the mainstream definition of Christianity for most Christians." The majority of churches in Christianity can trace their doctrine and practices from what was established at this council and from the Nicene Creed. The laws were codified, the Theodosian Code (wikipedia), and enforced on 1 january 439 CE later thus forming the Catholic (or universal) Christianity. The end result was a Christianity centered about sunday worship, Easter, and Christmas, see The Codex Theodosianus: On Religion.
Brad Scott (1953-2020) of WildBranch Ministries has a audio teaching - The History of the Church: on the ROCK or on the rocks? (audio, 1 hr 18 min).
All Christians should know the origin, major influences, and changes/history of their faith structure (religion).
Throughout history people have been "called out" from apostate religions, mainly from the Roman Catholic Church (and its "daughters"), toward a more truer form of obedience (worship). Many individuals and groups were called heretics (the Greek word for sects) by the church. John Foxe wrote his "History of the Acts and Monuments of the Church" in 1554, which is more commonly known as Foxe's Book of Martyrs (video, 58 min) and the online Foxe's Book of Martyrs. Many are described in The Pilgrim Church by E. H. Broadbent (1955), such as Priscillian who died in 385, and also Constantine, Simeon, Genesios, Joseph, Zacharias, Baanes, Sembat, and Sergius who all labored from about 650 to 850. Claudius of Turin (? to 827) wrote a lot and was attacked as a heretic. The Paulicians flourished between 650 and 872. In Italy, the Waldensians (wikipedia) were keeping the true beliefs from about 1177 to 1532, The Israel of the Alps - The Story of the Waldenses (2013, 29 min, part 1 of 3 which has an overview of the apostasy), Part 2 (29 min) and Part 3 (29 min). A similar group was the Pasagians (wikipedia, Italy, 11th century to 12th century). Then the Western Schism (wikipedia, 1378-1418) with leaders including John Wycliffe, Jan Huss, and Jerome.
The Protestant Reformation (wikipedia, 1517-1648) with leaders including William Tyndale, Martin Luther, and John Calvin sought to restore the role of Ieosus/Jesus (the) Christ as the Anointed (or Messiah); using the English-Greek name of Yahusha, Also, they kept the day of worship on sunday instead of returning to saturday or the true Shabat (based on the 7th day from the New Moon). The main result of the Protestant Reformation was the King James Bible (1611). Richard Baxter wrote extensively until 1687. John Wesley preached extensively and helped formed groups of Christians in the mid 1700s.
Adullam Films produced The Untold History of the Bible documentary series (which can be found on YouTube) - A Lamp in the Dark: The Untold History of the Bible (2009, 3 hr), Tares Among the Wheat (2012, 2 hr, 40 min), and Bridge to Babylon: Rome, Ecumenism and the Bible (~2016, 2 hr, 51 min). Parts 1 and 2 show how the Roman Catholic Church persecuted the protestant groups and other faiths (such as the Natsarim) and talk about the reformations. All three will likely be removed from YouTube due to copyright issues.
Another reformation, Pentecostalism, began in the late 1700s, to emphasize the Set-apart Spirit (Ruakh haKodash) of Yahuah within believers. It became more widespread in the 1900s, and is still going on today.
In the late 1800s other leaders emerged, such as Charles Taze Russell (1852-1916) and Ellen G. White (1827-1915). Russell formed the Bible Students around many scriptural truths in the 1870s. Joseph Rutherford took control after his death, added more doctrine, and changed the name to Jehovah's witnesses in 1931; see Jehovah's Witnesses. White helped establish the Seventh-Day Adventist Church (SDA) in 1863 and was a prophetic leader until her death; they keep the Sabbath on saturday (the 7th day of the calendar week). Leaders then took the SDA toward mainstream Christianity during her later years. Ellen G. White's writings, especially about a healthy lifestyle, are still relevant today. Both religions, however, follow along the broad road of Christianity.
Ellen G. White wrote in The Great Controversy (1858, part of the Conflict of the Ages series):
Wycliff, Huss, Luther, Tyndale, Baxter, Wesley, urged that all doctrines be brought to the test of the Bible and declared that they would renounce everything which it condemned. Against these men [of Yahuah] persecution raged with relentless fury; yet they ceased not to declare the truth. Different periods in the history of the church have each been marked by the development of some special truth, adapted to the necessities of Yahuah's people at that time. Every new truth has made its way against hatred and opposition; those who were blessed with its light were tempted and tried. Yahuah gives a special truth for the people in an emergency. Who dare refuse to publish it? He commands His servants to present the last invitation of mercy to the world. They cannot remain silent, except at the peril of their souls. Yahusha's ambassadors have nothing to do with consequences. They must perform their duty and leave results with Yahuah.
The Great Controversy, Chapter 38 (1911, sacred names substituted), see wikipedia's The Great Controversy (book).