Christianity has a history spanning approximately two thousand years. Originating in the 1st century CE in the Roman-controlled region of Palestine, it has grown into the religion with the largest number of followers in the world today. The following is a detailed overview of its historical development, divided into several key stages:

1. Early Christianity (1st–3rd centuries CE)

Christianity emerged in the early 1st century CE in Judea, then under the rule of the Roman Empire. Initially regarded as a branch of Judaism, it was centered on belief in Jesus, a Jewish teacher, as the Messiah (the Savior). After Jesus was crucified, his followers—especially the Twelve Apostles—began spreading his teachings, proclaiming that he had risen from the dead and ascended into heaven, becoming the Christ who redeems humanity.

Spread and Persecution

Early Christians were composed mainly of Jews and a growing number of Gentiles (non-Jews). The Apostle Paul (Paul of Tarsus) played a crucial role through his missionary journeys (recorded in the Acts of the Apostles), bringing Christianity to Asia Minor, Greece, Rome, and other regions. Christianity was unique in its universalist message—it was open to all people regardless of ethnicity, which contrasted with Judaism’s ethnonational character.

However, early Christians often faced persecution from Roman authorities for refusing to worship the emperor or pagan gods. For example, Emperor Nero blamed Christians for the Great Fire of Rome in 64 CE and initiated violent persecutions.

Organizational Development and Early Doctrine

As believers increased, the early church gradually formed a loose organizational structure, led by presbyters and bishops. In the 2nd century, Christianity encountered both internal and external challenges: internally from heretical movements (such as Gnosticism, which emphasized a dualism between spirit and matter), and externally from Roman suppression. In response, church leaders began compiling authoritative scriptures, laying the foundations for what would become the New Testament.

Turning Point: Legalization

In 313 CE, Emperor Constantine I and Eastern Emperor Licinius jointly issued the Edict of Milan, granting Christians freedom of worship. This marked Christianity’s transition from an underground movement to a legalized religion. Constantine himself later converted to Christianity and convened the First Council of Nicaea in 325 CE, which affirmed the doctrine of the Trinity and established foundational theological standards. In 380 CE, Emperor Theodosius I issued the Edict of Thessalonica, making Christianity the official state religion of the Roman Empire.

2. Medieval Christianity (4th–15th centuries)

With the fall of the Western Roman Empire in 476 CE, Christianity entered a new historical phase, becoming the central institution of medieval European society.

Rise of Church Authority

In Western Europe, the Bishop of Rome (the Pope) gradually emerged as a supreme religious—and often political—figure. Pope Leo I (440–461) strengthened papal primacy, while Pope Gregory I (590–604) expanded the Church’s influence through missionary work and monastic reforms. In the East, the Eastern Orthodox Church developed around Constantinople and was closely integrated with the Byzantine Empire.

The East–West Schism (1054)

Differences in culture, language (Latin vs. Greek), and theology (such as whether the Holy Spirit proceeds from the Father alone, or from both Father and Son) led to the formal schism of 1054. The Western Church became the Roman Catholic Church; the Eastern Church became the Eastern Orthodox Church. The division remains unresolved to this day.

Crusades and Expansion

From 1095 to 1291, the Catholic Church launched the Crusades to reclaim Jerusalem from Muslim control. Although largely unsuccessful militarily, the Crusades intensified contacts between Europe and the East and exposed the Church’s growing secularization and militarization.

Meanwhile, Christianity spread northward (to Scandinavia) and eastward through missionary efforts and monastic networks (such as the Benedictine Order).

Cultural and Intellectual Influence

The Church preserved classical learning (including Aristotle’s works) and helped develop scholastic philosophy. Thomas Aquinas (1225–1274), through his Summa Theologica, integrated faith and reason, forming the cornerstone of Catholic theology.

3. The Reformation and Early Modern Period (16th–19th centuries)

By the late Middle Ages, corruption and abuses within the Catholic Church—such as the sale of indulgences—sparked widespread dissatisfaction, eventually leading to the Protestant Reformation.

Martin Luther’s Reformation (1517)

In 1517, German monk Martin Luther posted the Ninety-Five Theses in Wittenberg, denouncing ecclesiastical abuses. He emphasized “justification by faith alone” and the supreme authority of Scripture over papal decrees. His challenge sparked the Protestant movement, gaining support from German princes and common people alike.

Rise of Protestant Denominations

John Calvin of Geneva developed the doctrine of predestination and emphasized God’s absolute sovereignty. King Henry VIII of England broke with Rome over marital issues and established the Anglican Church. Protestant groups generally rejected Catholic rituals and hierarchical priesthoods, resulting in diverse theological traditions.

Catholic Counter-Reformation

In response, the Catholic Church convened the Council of Trent (1545–1563), reaffirmed traditional doctrines, and instituted reforms. The Society of Jesus (Jesuits) was founded, becoming a major force in global missionary activity and education.

Global Expansion

With European colonial expansion, Christianity spread throughout the Americas (particularly Catholicism in Spanish and Portuguese territories), Africa, and Asia (e.g., the Philippines). However, missionary activities often accompanied colonial domination and sometimes involved coercive conversions.

4. Modern Christianity (20th–21st centuries)

From the 20th century onward, Christianity has experienced profound transformations under the influence of globalization, secularization, and technological advancement.

Ecumenical Movement and Interfaith Dialogue

The 1910 Edinburgh Missionary Conference initiated the ecumenical movement, promoting cooperation among Catholic, Protestant, and Orthodox churches. The Second Vatican Council (1962–1965) modernized Catholicism, allowing the use of vernacular languages in the Mass and encouraging engagement with contemporary society.

Rise of Evangelicalism and Pentecostalism

Evangelical and Pentecostal movements, emphasizing personal conversion and the gifts of the Holy Spirit, have grown rapidly in the United States, Africa, and Latin America. Figures such as Billy Graham influenced millions through large-scale evangelistic campaigns.

Secularization and Challenges

In Europe and North America, secularization has led to a decline in church attendance, with many turning to atheism or non-religious spirituality. Church scandals—such as sexual abuse cases within the Catholic clergy—have further undermined credibility.

Conversely, Christianity continues to expand vigorously in Africa (e.g., Nigeria) and Asia (e.g., South Korea).

Status as of 2025

As of early 2025, Christianity has approximately 2.4 billion adherents, representing about 31% of the global population. Growth is concentrated in developing countries, while Western nations face pressures from pluralism and secularization.