What is the history of 'The United Church of God'?

Herbert W. Armstrong was raised a Quaker but was not especially religious. His wife associated with some Seventh Day Adventists, and after he called them fanatics, she gave him a challenge to prove, from the Bible the doctrine of observing the sabbath on Sunday. He took up the challenge, studied and research the topic endlessly, and eventually had to admit that his wife was right, there really was no biblical support for Sunday.

Having discovered that what he had considered one of the fundamental doctrines of Christianity wasn't Biblical, he became obsessed with the idea and began researching other doctrines. When most of them too fell in turn, he himself became what others might call a religious fanatic, and began preaching the truths that he had discovered, at first locally and then on a radio program.

He felt that God was leading him to the truth, but never did he claim to have received any divine revelations, prophecies, or new truths. The truth was there in the Bible for everyone to see, if they were only willing to read it for themselves. Many times he would say, "Blow the dust off your Bible and prove it for yourself. Don't believe me, believe the Bible.".

Armstrong did not teach that he had founded a new church or found a new truth. The religion he preached was a continuation of the same small church that has has existed since the days of the Apostles. See A TRUE History of the TRUE CHURCH by Herman L Hoeh, 1959.

To promote this truth, he published The Plain Truth magazine and founded the Radio Church of God in 1933. This later became the Worldwide Church of God, with radio and television programs around the world in many languages. The magazine's subscriptions were exceeded only by TV Guide.

The Autobiography of Herbert W. Armstrong is available for online viewing, downloadable, or as a printed book (over 900 pages).

His son, Garner Ted Armstrong, was his heir apparent, and in the 1970s was the face on "The World Tomorrow" television program. By 1978 though, internal disagreements in the organization led to GTA's excommunication, and his founding of the Church of God International, which had effectively the same religious doctrines as the original church.

HWA continued leading the WCG until his death in 1986. During that time he continued as an ambassador for Christianity. He was also recognized as an ambassador for world piece, being received by hundreds of political leaders around the world. "Mr. Armstrong contributed to sharing the word of the Lord with his community and with people throughout the nation. You can take pride in his legacy." — U.S. President Ronald Reagan

Church membership exceeded 100,000 tithe-paying members. The Church and its teachings had an appeal to intelligent and logical thinking people, rather than the emotional appeal used by most other denominations.

His book, Mystery of the Ages, published in 1985 was a summary of the church's doctrines. This book, like all their publications, was sent free of charge to anyone that requested it. The organization never solicited anyone but their own members for donations.

Following HWA's death, the church continued in the same path for a few years, but then began a process of changing their doctrines, revising, dropping, or charging for their publications, and generally moving toward mainstream Christianity. Many in the ministry objected to this direction, and over the next few years the vast majority of them broke away at various times, forming their own denominations, each claiming to be a true continuation of Armstrong's teaching.

The remaining church, which by now had accepted Sunday worship, the Trinity, unclean food, Christmas, and just about every doctrine that distinguished the original church from mainstream Christianity, renamed itself to Grace Communion International. The church was now much much smaller and far far richer, having sold off the assets that had belonged to the much larger organization (e.g. Bible college campuses in England and California), and the luxurious Ambassador Auditorium in Pasadena, whose acoustics were so perfect that many artists (e.g. Arthur Rubenstein and Herbert von karajan) refused to perform anywhere else on the west coast.

(The Wikipedia article on the Worldwide Church of God is extremely bad, making it look like the original church saw the error of its ways and finally managed successfully to join the National Association of Evangelicals.)

Meanwhile, the spinoff churches continued to grow and promote the truth, again giving freely to all that asked. Some accept each other as equally legitimate parts of God's Church; others don't.

There are many smaller groups, but the United Church of God is probably the largest and most conservative, along with the Living Church of God. The Reformed Church of God and the Philadelphia Church of God are much stronger on applying prophecy to specific current events and have in some ways made additions to the original beliefs. Most differences appear to be over leadership rather than doctrine though.

The Philadelphia Church of God continued publishing Herbert W. Armstrong's books and booklets, and was sued by Grace Communion International for copyright violation. The issue wasn't that the copyright holders were demanding royalties for the publication (the PCG would have willingly paid), but that they were using copyright law to suppress the publication of material they disagreed with. The case made its way to the US Supreme Court WORLDWIDE CHURCH OF GOD v. PHILADELPHIA CHURCH OF GOD INC

Unfortunately, the PCG ended up losing that case (the minority report is worth reading), but surprisingly the winning side later simply sold the copyright to them. The entire story of this court battle (and the church history summarized above and much more) is described in full in Raising the Ruins.

That book, and the others linked above thanks to the copyright purchase, are all provided free of charge by the Philadelphia Church of God.

Disclaimer: I have never been a member of any of the organizations mentioned or implied above. I do however find their doctrines, derived by biblical exegesis without using tradition or other non-biblical sources, to be far more logically consistent and simpler than any other denomination I've encountered.