1. The Apostolic Age and Early Expansion (30–100 CE)

Christianity emerged after the death of Jesus Christ, as his followers—especially the apostles—began preaching in the region of Palestine under Roman rule.

The Founding of the Church in Jerusalem

After Jesus’ resurrection, the disciples gathered in Jerusalem, where Peter became the early leader. According to the Acts of the Apostles, the Holy Spirit descended on Pentecost, leading to about 3,000 people being baptized—an event regarded as the birth of the Church. Early Christians were predominantly Jews who continued to observe Jewish customs (such as the Sabbath), but their belief that Jesus was the Messiah led to conflict with mainstream Judaism.

Evangelization Among the Gentiles

The Apostle Paul (originally Saul), was pivotal. Initially a Pharisee persecuting Christians, he converted after experiencing a vision of the resurrected Jesus on the road to Damascus (c. 34–36 CE). Paul then dedicated himself to preaching to Gentiles (non-Jews). His three missionary journeys (c. 46–58 CE) took him across Asia Minor and Greece—for example, to Philippi and Corinth—and eventually to Rome, where he established multiple churches. His epistles (e.g., Romans, 1 Corinthians) later became central texts of the New Testament.

Persecution and Growth

Christians frequently faced persecution for rejecting Roman polytheism. In 64 CE, Emperor Nero notoriously blamed them for the Great Fire of Rome, sparking brutal repression. Yet persecution only encouraged further spread, attracting slaves and lower-class citizens. By the end of the 1st century, Christianity had reached major cities across the eastern Roman Empire.

2. Institutional Formation and Doctrinal Consolidation (100–500 CE)

As Christian numbers increased, the religion developed into an organized institution with defined doctrines.

Development of Church Organization

By the 2nd century, a hierarchical structure emerged: bishops oversaw regions, elders assisted in administration, and deacons served the community. Episcopal authority strengthened over time, with the Bishop of Rome asserting succession from Peter. Meanwhile, the New Testament canon gradually formed, with the four Gospels and Paul’s epistles widely accepted.

Doctrinal Debates and Councils

The early Church faced numerous theological challenges, such as:

Gnosticism, which emphasized spiritual knowledge and denied bodily resurrection

Arianism, which denied that Christ was of the same substance as God the Father

In 325 CE, Emperor Constantine convened the Council of Nicaea, which established the doctrine of the Trinity, affirming that the Father, Son, and Holy Spirit are equal and consubstantial. The Council of Constantinople (381 CE) further solidified this dogma.

Legalization and Becoming a State Religion

The Edict of Milan (313 CE) legalized Christianity and ended large-scale persecution. In 380 CE, Theodosius I issued the Edict of Thessalonica, declaring Christianity the only legitimate religion of the Roman Empire. From this point forward, Church and imperial authority became closely intertwined.

3. Unity and Division in the Middle Ages (500–1500 CE)

The Middle Ages marked the golden age of Christianity in Europe, where the Church became the center of culture, politics, and religion.

The Catholic Church in Western Europe

After the fall of the Western Roman Empire (476 CE), the Catholic Church filled the resulting power vacuum. Pope Gregory I (r. 590–604) sent missionaries such as Augustine of Canterbury to evangelize England, fueling Christianization in northern Europe. In the 8th century, the Pope allied with the Frankish kingdom; in 754 CE, King Pepin the Short granted land to the Pope, forming the Papal States. Monastic orders—such as the Benedictines—preserved scholarship and advanced evangelization.

Eastern Orthodoxy

In the Byzantine Empire, Eastern Orthodoxy developed in close cooperation with imperial authority. The Bishop of Constantinople (later “the Ecumenical Patriarch”) led the Eastern Church, which emphasized liturgy and mystical theology. In 1054, disputes over doctrine (e.g., the “Filioque” clause), culture (Greek vs. Latin), and political authority culminated in the Great Schism, formally splitting the Church into Roman Catholicism and Eastern Orthodoxy.

The Crusades and Expansion

Between 1095 and 1291, the Catholic Church launched the Crusades to reclaim the Holy Land from Muslim control. Although militarily unsuccessful, they stimulated East–West trade and cultural contact. Christianity also expanded into Eastern Europe (e.g., Russia—Kievan Rus’ was baptized in 988) and northern Europe.

Scholasticism and Crisis

In the 13th century, Thomas Aquinas and others developed Scholasticism, an effort to harmonize reason and faith. Yet by the late Middle Ages, corruption in the Church (e.g., simony) and excessive power triggered widespread dissatisfaction—setting the stage for the Reformation.

4. The Reformation and the Rise of Christian Pluralism (1500–1800 CE)

The 16th-century Reformation radically transformed Christianity, dividing it into Catholicism and Protestantism.

Martin Luther’s Challenge

In 1517, Martin Luther posted the Ninety-Five Theses, criticizing the Catholic practice of selling indulgences. He advocated justification by faith and the authority of Scripture. In 1521, he was excommunicated but gained the support of German princes, eventually founding Lutheranism.

Expansion of Protestant Branches

Calvinism: John Calvin promoted the doctrine of predestination and God’s absolute sovereignty in Geneva, influencing Scotland (Presbyterianism) and France (Huguenots).

Anglicanism: In 1534, Henry VIII broke with Rome over marital disputes, establishing the Church of England.

Radical Reformers: Groups like the Anabaptists advocated adult baptism and separation of church and state.

The Catholic Counter-Reformation

The Council of Trent (1545–1563) reaffirmed Catholic doctrine—including the sacraments and papal authority—and reformed internal corruption. The Jesuits were established as a key force in education, missions, and theological defense.

Global Spread

Catholicism spread through Spanish and Portuguese colonization to Latin America and Asia (e.g., the Philippines). Protestantism spread through Dutch and British expansion to North America and parts of Africa.

5. Modernization and Globalization (1800–2025 CE)

Since the 19th century, Christianity has adapted to industrialization, secularization, and globalization, becoming a diverse world religion.

Missionary Movements

Protestant missionaries such as William Carey spread Christianity to Africa, Asia, and the Pacific alongside Western colonial expansion. Catholicism strengthened its foothold in Latin America.

Ecumenism and Modern Reforms

The 20th century saw efforts toward Christian unity. The 1910 Edinburgh Missionary Conference led to the modern ecumenical movement. The Second Vatican Council (1962–1965) modernized Catholicism, allowing local languages in the Mass and promoting openness to the contemporary world.

Rise of Evangelicalism and Pentecostalism

Evangelicalism emphasizes personal conversion and biblical authority. Pentecostalism—originating in the 1906 Azusa Street Revival in the U.S.—emphasizes spiritual gifts such as healing and speaking in tongues. Together, they have grown rapidly in Africa, Latin America, and Asia.

Secularization and Challenges

In Europe and North America, Enlightenment rationalism, scientific advancements, and secular culture weakened church influence, leading to declining attendance. Scandals—such as clerical sexual abuse—further damaged church credibility. Nevertheless, Christianity continues expanding in Africa (e.g., Nigeria) and parts of Asia (e.g., South Korea).

Status as of 2025

As of February 26, 2025, Christianity has approximately 2.4 billion adherents, representing 31% of the world’s population. Its demographic center has shifted from Europe to the Global South, with Africa and Latin America serving as the primary engines of growth.