Bible events are mentioned outside the Bible:
1208 BC. An Egyptian stone boasts of successful warfare against groups in Palestine, mentioning Israel by name. (The Merneptah Stele ）
900’s BC. Two sliver scrolls have been found from this time period in Jerusalem, on which are the words of Numbers 6:25.
930 BC. An Egyptian stone boasts of successful warfare against the King of Israel, the same battle mentioned in the Bible at First Kings 14:25-26. (Pharoah Shesonk, also spelled Shishak)
850 BC. A stone from today’s Jordan mentions occupying some of Israel’s territory during the time of Israelite king Omri and his son Joram, and this stone mentions the Israelite’s name for God. This conflict is referred to in Second Kings 8:20-22. (Moabite stone)
Bible Prophecies that have already come true
The Bible prophet Ezekiel said that the city of Tyre would be destroyed (Ezekiel 26:1-14). Alexander the Great destroyed Tyre 250 years later.
The Bible prophet Isaiah said that Babylon would be destroyed (Isaiah 13:19). 600 years later the Roman emperor Julian had its walls destroyed.
Prophecies about Jesus.
The prophet Micah said the savior would be born in Bethlehem, and 400 years later Jesus was born there (MIcah 5:2)
Psalm 22, a Psalm of David, spoke about hands and feet being pierced (verse 16), and dividing up clothes by casting dice (verse 18). These things came true while Jesus was on the cross.
The prophet Isaiah spoke about the savior dying for sins (Isaiah 53::5-6, and 11-12), being buried in a rich man’s tomb (verse 9), and rising from the dead (verse 10).
(there are dozens of prophecies about Jesus)
The New Testament
On the origin of the New Testament: most of it was written before the Romans destroyed Jerusalem in 70 AD, so it was subject to examination by eye-witnesses to the events. We have documents from the early church that make references to the New Testament, so we know it was gathered early-on into gospels and epistles. A letter written in 76 AD mentions Jesus and Peter, and refers to the teachings of Paul (First Epistle of Clement to the Corinthians). A letter called “the Epistle of Barnabas,” written between 70 and 100, says that “Christ is present in the Old Testament just as much as He is in the New. (Masterpieces of Christian Literature, ed. Frank N McGill, New York, Harper and Row, 1963, pages 1 and 5). Justin Martyr, writing in 150, refers to the “memoirs of the apostles” and includes among them the gospels. A leader named Irenaeus, written in 180, refers to “the four gospels.” http://en.wikipedia.org/wiki/Christianity_in_the_2nd_century. (scroll down to “Writings.”) The gospels and epistles were known to the church in the second century, and the only question was whether to include Hebrews, James, and 2nd Peter. This was resolved before 367, since a document of the year 367 includes the same list of books as we still use today.
Roman secular writers
Roman officials were aware of Christians and mention them in their writings. Two examples:
The Roman historian Tacitus wrote that emperor Nero punished the Chrstians. He adds that Christ “was executed at the hands of the procurator Pontius Pilate in the reign of Tiberius.”
The Roman governor Pliny around the year AD 112 described the Christians: “on an appointed day they had been accustomed to meet before daybreak and recite a hymn to Christ, as to a God.”
Christians have not altered the New Testament:
There are thousands of hand-written copies, with short portions as old as the 100’s http://en.wikipedia.org/wiki/New_Testament#Early_manuscripts
These versions have been compared, and the differences are in such areas as spelling mistakes and grammar, and none of them affect Christian teachings.
God as “three-in-one” (the Trinity) was believed from early on
The Father, Son, and Holy Spirit are cited in Matthew 28:19.
Irenaeus, a Christian leader writing around 180, quotes this early version of the creed: … this faith: in one God, the Father Almighty, who made the heaven and the earth and the seas and all the things that are in them; and in one Christ Jesus, the Son of God, who was made flesh for our salvation; and in the Holy Spirit, who made known through the prophets the plan of salvation, and the coming, and the birth from a virgin, and the passion, and the resurrection from the dead, and the bodily ascension into heaven of the beloved Christ Jesus, our Lord, and his future appearing from heaven in the glory of the Father to sum up all things and to raise anew all flesh of the whole human race … : http://en.wikipedia.org/wiki/Rule_of_Faith