When we use the term "Great Tribulation", we are referring to a period of suffering that the world will be exposed to in the last days coinciding with the judgment of God upon the Antichrist and his government (see Revelation 6:1-17). Some theologians think that the Tribulation has already taken place. There was a great persecution of Christians and Jews during the Roman Empire. It is true, too, that some theologians believe that the Tribulation refers only to Israel or the Jewish people, and not to Christians or the rest of the world. If we assume that the Tribulation will be a future worldwide time of persecution, then Christians will indeed go through it. The Bible does not suggest that Christians will be "raptured" prior to the Tribulation.
The Bible teaches two comings of Jesus--one, His birth; the second, His coming again in triumph. There is no third coming for a secret rapture. The book of Matthew specifically says, "Immediately after the tribulation of those days. ... Then the sign of the Son of Man will appear in heaven ... And He will send His angels ... And they will gather together His elect from the four winds, from one end of heaven to the other" (Matthew 24:29-31).
This is just one of many references that indicate we will be going through a time of tribulation until Jesus Christ comes back (see John 16:33, Romans 8:35, Revelation 7:13-14).
Christians will be protected in the midst of tribulation, however. After all, the Israelites were protected when the plagues fell upon Egypt. God knows how to make a distinction between His people and those who are not His people. He allowed sorrow and suffering to rain upon the ungodly in Egypt while He caused the children of Israel to prosper.
But we must recognize also that the devil and his emissaries despise Christians. There has always been a struggle between the people of God and those who serve Satan. Throughout history there have been successive martyrdoms of Christians, and it is the height of arrogance to assume that only 21st century Christians in the United States of America will be spared any kind of persecution. That goes against the flow of history for the last 2,000 years. The book of Revelation speaks of Tribulation martyrs--those who were slain for the witness of Christ--standing near the great throne of God and crying out, "How long ... Until You judge and avenge our blood on those who dwell on the earth?" (Revelation 6:9-10) So there will be people during the Tribulation who love Jesus, and who will give their lives for Him.
Jesus said, "He who endures to the end shall be saved" (Matthew 24:13). Persecution is simply part of living as a Christian in this world. Saints around the world have been tortured, have suffered privation and have had their jobs and their families taken away from them. Many of them have died because of their witness for Jesus. It is hard to contemplate much worse tribulation than these great men and women of faith have already endured.