From https://en.wikipedia.org/wiki/Great_Controversy_theme :
In Seventh-day Adventist theology, the Great Controversy theme refers to the cosmic battle between Jesus Christ and Satan, also played out on earth. Ellen G. White, a co-founder of the Seventh-day Adventist Church, delineates the theme in her book The Great Controversy, first published in 1858. The concept, or metanarrative, derives from many visions the author reported to have received, as well as from scriptural references. Adventist theology sees the concept as important in that it provides an understanding of the origin of evil, and of the eventual destruction of evil and the restoration of God's original purpose for this world. It constitutes belief number 8 of the church's 28 Fundamentals.
Adventist Theologian Herbert E. Douglass writes that Calvinistic-leaning Christians view this theme and the Adventist movement that produced it as heterodox.