Indeed - the Orthodox Church probably would never have called an ecumenical council had it not been for the nightmare caused by Arius and his supprters in the aftermath of the edict of Milan, and their continued contumacy after Pope St. Alexander of Alexandria anathematized Arianiasm and deposed Arius. And there wouldn’t have been a second ecumenical council without people like Eusebius of Nicomedia conspiring to convert the heir apparent, Constantius, to the Arian religion, away from Christ, and to perpetuate the heresy of Arius even after Arius was struck down by what many believe was a providential act, just before Arius was to be allowed to receive communion in the Hagia Sophia according to one of the ancient Synaxaria.
Indeed by the Second Ecumenical Council there were multiple Arian denominations - the Eunomians, the semi-Arians, the Pneumatomachs, and other screwball groups such as the Apollinarians, who were the first to confuse the humanity and divinity of our Lord, God and Savior Jesus Christ, compromising the doctrine of the Incarnation, which would later be continued by the Eutychians, who degenerated into Tritheism by the time of John Philoponus, the last known intellectual of the original Monophysites (the group following Eutyches that was anathematized both by the Chalcedonians and the non-Chacledonians). Interestingly the modern successor to that group is probably the Mormons, insofar as Mormons are tritheistic, and Eutychianism promotes Tritheism by comingling the humanity and divinity in the prosopon of the Logos.
Then the Monothelites were actually created for the most farcical of reasons - an attempt to heal the schism between the Eastern Orthodox and the Oriental Orthodox, by basically reinventing Apollinarianism. This did not work, the only lasting result being the schism of the Monothelite Maronites of Lebanon from the Syriac Orthodox - the Maronites later entered into communion with the Roman Catholic Church and the Syriac Orthodox have a formal agreement with the Antiochian Orthodox since 1991 (which I’ve been told is not in force in North America, which makes sense, because AOCNA is an autonomous church under the omophorion of the Antiochian Orthodox Patriarch, His Beatitude John X Yazigi, for the Antiochian emigres and other Arabic speaking Orthodox Christians were served by the ministry of St. Rafael of Brooklyn, an Antiochian bishop transferred canonically to the Russian Orthodox Church, which was widely regarded as the canonical church in North America prior to the confusion and chaos that followed the Bolshevik revolution, which resulted in the Russian church splitting into three Slavic groups, which became ROCOR, the Metropolia (later the OCA) and the Patriarchal Parishes, and likewise caused a schism among the ethnically Syrian Christians who had been under the pastoral care of the Metropolitan of New York and North America (historically St. Tikhon of Moscow, the first Patriarch since Nikon, and the last for well over a decade, who died in a Soviet prison in the early 1920s, where he was treated harshly) and until his repose in 1915, St. Rafael of Brooklyn.
Interestingly there was also a schism among the Armenians after the USSR invaded that country. The Communists caused a massive number of schisms, almost all of which have healed, thankfully, because people became fearful that the church authorities had been corrupted by the secret police - a legitimate concern.
One group I have very little patience for are the small minority of ROCOR members who left ROCOR and joined schismatic groups like the “Genuine Orthodox Church” after schism separating ROCOR from the MP and the other canonical churches including the OCA was healed in a glorious moment in 2007. But what for most Orthodox was a moment of great happiness, was for a small misguided minority an occasion for sinful despair and schism.