Many different groups of Christians or churches exist in the world today. The Roman Catholic Church accounts for over half of the Christians in the world, and they recognize the Pope as their leader. The other two main groups are the Orthodox Church and the Protestants. Though these Christian groups often disagree, they have 3 main areas of agreement: Jesus, Worship, and the Bible.
Jesus, the son of Mary and Joseph, was born in Bethlehem during the time of the Roman occupation. During the last three years of his life he preached about love, compassion, forgiveness, and His Father, God. He had a large following of disciples. Many Jews thought he would be the Messiah who was proclaimed to save humankind from its sin. With his disciples Jesus traveled around and performed healing miracles and showed His power over nature. These stories can be read in the New Testament of the Bible. He criticized the authorities of the day and eventually was unjustly crucified by Pontius Pilate. Jesus then rose from the dead three days after he died: the Resurrection which is celebrated during Easter. Forty days after his resurrection, Jesus ascended into heaven where he lives with his Father and the Holy Spirit.

Jesus predicted His death at His Last Supper with his disciples. During this last supper together, He wanted His disciples to share bread and wine with Him. Each of these elements represents a portion of the suffering: the bread - His body which would be broken, and the wine - His blood which would be spilt out for the sins of humankind. Most Christian churches remember this event through a ceremony known as the Mass, Eucharist, Holy Communion, or The Lord’s Supper. In addition, all Christians use the “Bible, hymns, sermons, and personal and group prayer as part of their worship.”
The Bible is God’s Word to humankind that He inspired ordinary men to write. The Bible is divided into the Old Testament (creation story, history of the Jews and their relationship with God, Ten Commandments) and the New Testament (the life of Jesus, the story of Pentecost the disciples received the power of the Holy Spirit and Paul’s advice to Christian communities on the problems that they were facing.)

Concepts of God
Christians believe in one God (monotheism) who created the world and all humans and so has power over it and them. He created the world for a purpose and He knows each individual’s destiny. Christians believe that each individual has free will to choose if they want to reject or accept the will of God. Christian understanding of God is founded in the Bible and is dictated in the idea of the Trinity (three-person-in-one being): God as Father, God as Son, and God as Holy Spirit. While the three Persons are each God, each is distinct from the others. No one has ever seen God, but many people have seen God the Son in human flesh through Jesus who lived on earth in the Middle East. The Bible tells us that to know and see what God is like, we must look at the earthly life of Jesus.

Some of His attributes include:
compassion towards people
forgiveness of people’s sin
wrath at hypocrisy and injustice
power to control the elements of nature
concern about every person individually
leading by serving others
showing the only way to find God
Human beings are unique and wonderful creations of God and not an accident from the evolutionary process. Consequently, no one is ever conceived or born as an accident in God's eyes. We all have the potential to live either a productive or a destructive life somewhere between the extremes of Adolf Hitler and Mother Teresa. Every person during the course of his/her lifetime has the opportunity to have a relationship with God. Sin is the only thing that hinders that relationship and so the need for confession and repentance.

God as Father: Christians believe that God lives in Heaven, as stated in the Lord’s Prayer. The image of God as Father is very important to Christians and is also repeated in the belief of the church. When referring to God as Father, it is not to be confused with the earthly notion of fathers but instead an image of the perfect Father in perfect harmony with his children. God the Father loves, cares for, and disciplines his children when they have done wrong. Christians believe that God is their judge and they see it as their duty to please him.

God as Son: Jesus, born in Bethlehem about 2,000 years ago, was the son of Mary and also of God. This Immaculate Conception which resulted in the incarnate (God born as human) birth of God the Son, is important for the Christian faith. Because He lived as a human, He knows what it is to suffer and to experience temptation, even though He did not succumb to sin. Jesus’ power is told in the Bible through stories of miracles and His resurrection.
God as Holy Spirit: Jesus sent His Holy Spirit (Holy Ghost) to help and guide the disciples after He ascended to Heaven. It is physically represented by a dove. Christians believe that God’s Holy Spirit lives within them after they are “saved” in order to help guide them through life.

The Numbers

With an estimated number of adherents that ranges approximately around 2.1 billion, split into 3 main brances of Catholic, Protestant and Orthodox, Christianity is the world's largest religion. The Christian share of the world's population has stood at around 33 per cent for the last hundred years. This masks a major shift in the demographics of Christianity; large increases in the developing world (around 23,000 per day) have been accompanied by substantial declines in the developed world, mainly in Europe and North America (around 7,600 per day). It is still the predominant religion in Europe, the Americas, the Philippines, and Southern Africa. However it is declining in many areas including the Northern and Western United States, Oceania (Australia and New Zealand), northern Europe (including Great Britain, Scandinavia and other places), France, Germany, the Canadian provinces of Ontario, British Columbia, and Quebec, and parts of Asia (especially the Middle East,South Korea, Taiwan and Macau).

In most countries in the developed world, church attendance among people who continue to identify themselves as Christians has been falling over the last few decades. Some sources view this simply as part of a drift away from traditional membership institutions, while others link it to signs of a decline in belief in the importance of religion in general.

-Christianity exists in Europe, North America, Latin America, Africa and parts of Asia. One would expect this given that it is a universal religion.
-Given that it exists in many stage 4 countries, this might explain why it has a slower growth than Islam as a percentage (stage four have less population growth and are increasingly secular)
-It is the largest universal religion
-there are many differing branches and sects of this religion

-first diffused through relocaton diffusion of missionaries
-people from the well-connected cities along the trade routes heard the message first (relocation)
-it then spread to all of the areas around the cities and the Roman empire (contagious)
-the word pagan actually means countryside because they were the last to believe Christianity and they believed in multiple gods.
-it has also spread to other parts of the world through migration, missionary activity and colonialism from the 1500s forward
-waves of migration have caused a set dispersal pattern of differing Christians in America --Catholics in areas like Boston and Chicago where Italians, Irish and certain eastern Europeans migrated -Lutherans in areas where Scandinavians and Germans migrated like the northern Midwest -French Catholics in Quebec -Catholics in the southwest -Mormons to Utah due to persecution in New York.