In the Assyrian homeland, Chaldean Catholics primarily inhabited villages and cities that are located in what is now modern day Iraq, such as Alqosh, Ankawa, Araden, Baqofah, Batnaya, Karamlesh, Mangesh, Shaqlawa, Tesqopa, Tel Keppe, and Zakho.

In 1881, archeologist and author Hormuzd Rassam stated: “The inhabitants of Assyria consist now of mixed races, Arabs, Turkomans, Koords, Yezeedees, Jews, and Christians called Chaldeans and Syrians.

The Council condemned as heretical the Christology of Nestorius, whose reluctance to accord the Virgin Mary the title Theotokos "God-bearer, Mother of God" was taken as evidence that he believed two separate persons (as opposed to two united natures) to be present within Christ.

Under the influence of Barsauma, Bishop of Nisibis, the Church of the East officially accepted as normative the teaching not of Nestorius himself, but of his teacher Theodore of Mopsuestia, whose writings the 553 Second Council of Constantinople condemned as Nestorian but some modern scholars view them as orthodox.

[45] After its split with the West and its adoption of a theology that some called Nestorianism, the Church of the East expanded rapidly in the medieval period due to missionary work.

Around 1400, the Turco-Mongol nomadic conqueror Timur arose out of the Eurasian Steppe to lead military campaigns all across Western, Southern and Central Asia, ultimately seizing much of the Muslim world after defeating the Mamluks of Egypt and Syria, the emerging Ottoman Empire, and the declining Delhi Sultanate.

After the destruction brought on by Timur, the massive and organized Church of the East structure was largely reduced to its region of origin, with the exception of the Saint Thomas Christians in India.

[57][55][66] Shimun VIII Yohannan Sulaqa returned home in the same year and, unable to take possession of the traditional patriarchal seat near Alqosh, resided in Amid.

For various reasons, including the ecclesiastical as well as political turbulence in Europe after the French Revolution, Rome was long unable to choose between two rival claimants to headship of the Chaldean Catholics.

[68] In 1793 it was agreed that Yohannan should withdraw from Amid to Mosul, the metropolitan see that he already held, but that the post of patriarch would not be conferred on his rival, Joseph IV's nephew.

[72] In the 21st century, Father Ragheed Aziz Ganni, the pastor of the Chaldean Church of the Holy Spirit in Mosul, who graduated from the Pontifical University of Saint Thomas Aquinas, Angelicum in Rome in 2003 with a licentiate in ecumenical theology, was killed on 3 June 2007 in Mosul alongside the subdeacons Basman Yousef Daud, Wahid Hanna Isho, and Gassan Isam Bidawed, after he celebrated mass.

[82] Despite the internal discords of the reigns of Yohannan Hormizd (1830–1838), Nicholas I Zaya (1839–1847) and Joseph VI Audo (1847–1878), the 19th century was a period of considerable growth for the Chaldean church, in which its territorial jurisdiction was extended, its hierarchy strengthened and its membership nearly doubled.

[83] Paulin Martin's statistical survey in 1867, after the creation of the dioceses of Aqra, Zakho, Basra and Sehna by Joseph Audo, recorded a total church membership of 70,268, more than three times higher than Badger's estimate.

Most of the population figures in these statistics have been rounded up to the nearest thousand, and they may also have been exaggerated slightly, but the membership of the Chaldean Catholic Church at this period was certainly closer to 70,000 than to Badger's 20,000.

According to Chabot, there were mission stations in the town of Serai d’Mahmideh in Taimar and in the Hakkari villages of Mar Behısho, Sat, Zarne and 'Salamakka' (Ragula d'Salabakkan).

With around 100,000 believers in 1913, the membership of the Chaldean church was only slightly smaller than that of the Qudshanis patriarchate (probably 120,000 East Syriac Christians at most, including the population of the nominally Russian Orthodox villages in the Urmi district).

[citation needed] Tfinkdji's statistics also highlight the effect on the Chaldean Catholic Church of the educational reforms of the patriarch Joseph VI Audo.

The Chaldean Catholic Church on the eve of the First World War was becoming less dependent on the monastery of Rabban Hormizd and the College of the Propaganda for the education of its bishops.

Six bishops were educated at the College of the Propaganda (Joseph Gabriel Adamo, Toma Audo, Jeremy Timothy Maqdasi, Isaac Khudabakhash, Theodore Msayeh and Peter Aziz).

Over the years, the congregation has grown to nearly 100 sisters serving in various locations, including Iraq, Lebanon, Rome, Australia, the United Arab Emirates, Detroit, Chicago, Arizona, Turlock, and San Diego.

In 2022, the Chaldean Sisters celebrated their 100th anniversary with a fundraiser event to support their education expenses and the formation and novitiate home in Farmington Hills, Michigan.

A slight reform of the liturgy was effective since 6 January 2007, and it aimed to unify the many different uses of each parish, to remove centuries-old additions that merely imitated the Roman Rite, and for pastoral reasons.

In 1994, Pope John Paul II and Patriarch Dinkha IV of the Assyrian Church of the East signed a Common Christological Declaration.

[100][35][101] Chaldean Catholics largely bear the same family and personal names, share the same genetic profile, hail from the same villages, towns and cities in northern Iraq, southeastern Turkey, northeastern Syria and northwestern Iran, as their neighbours of other religious denominations.

In 1908, before the Assyrian genocide, the dissolution of the Ottoman Empire and the creation of new states in the Middle East such as Iraq, an article in the Catholic Encyclopedia states: "Strictly, the name of Chaldeans is no longer correct; in Chaldea proper, apart from Baghdad, there are now very few adherents of this rite, most of the Chaldean population being found in the cities of Kirkuk, Erbil, and Mosul, in the heart of the Tigris valley, in the valley of the Zab, and in the mountains of Kurdistan.

Such stances have often been detrimental to the political situation of Chaldean Catholics living in Iraq, and have threatened previous actions such as the Common Christological Declaration.

[106] We call upon our daughters and sons to reject these labels, to adhere to their Chaldean identity without fanaticism, and to respect the other names such as ‘Assyrians’, ‘Syriacs’, and ‘Arameans’.

We call upon the authorities in the region to respect them, and we encourage our Chaldeans to cooperate with everyone for the common good and not to split into unidentified groups or follow illusory projects that harm Christians.

In an effort to restore harmony, Cardinal Sako issued an ultimatum on August 28, 2024, requesting a public apology from the dissenting bishops by September 5.

This perception of Warda's ruthless power play has forced Sako to abandon his retirement plans and protect the Chaldean Catholic Church, despite his previous commitment to step down at 75.