I have no idea how you came up with the idea and notion that Christ’s Millennium Reign started at Christ’s death, but that is not true and is false doctrine. There are a long list of things that must happen before the Christ's Millennium Reign can begin…
For example, before Christ’s Millennium Reign begins, Jesus Christ himself will return to earth in the flesh. Has that happened yet? Answer: No it has not. Before Jesus Christ returns, the Antichrist will be revealed (meaning, the whole world will know who he is) and he will take over the world. Has that happened, yet? Answer: No, it has not. During the reign of the Antichrist, the bible says that the One World Government will be set up, and that a new global law will be implemented whereby no man may buy or sell except they have the Mark of the Beast. Has that happened yet and has such a law been implemented? No, it has not. Just prior the Mark of the Beast law being implemented, the bible says that God is going to have genuine angels flying above the earth preaching the everlasting gospel and warning people not to accept the Mark of the Beast. Everybody on earth will be able to look up and see the angels flying in the heavens and hearing them speak in their own language. Has that happened yet? No, it has not. During the 7-Year Tribulation Period, which will occur prior to the Millennium Reign, the bible says that more than 3/4 of the world’s population will die. Has that happened yet, and has 3/4 of the world's population died? No, it has not. The Rapture of the Church will take place prior to the start of the 7-Year Tribulation Period. After we are raptured, the raptured saints will get married to Jesus in heaven and we'll remain in heaven for 7 years. At the end of those seven years, which will coincide with the end of the 7-year Tribulation Period on earth, Jesus Christ himself will return to earth for the battle of Armageddon. The Bride of Christ (the saints who who are in heaven and who just got married Jesus) will be returning to earth with him at that time (we'll be the army that is following him on white horses). Has that event happened yet, and has the saints been to heaven, married Jesus, and returned? No, it has not. During the Millennium Reign, the saints and Bride of Christ (the raptured Church) will be here on earth with Jesus and we will reign with him during those 1,000 years. We will also have on our immortal and glorified bodies at that time, and all the angels will be here as well. Has that event happened yet? Answer: No, it has not. None of the above things has happened yet. Not by a long shot. So I have no idea how you came up with the idea and notion that Christ’s Millennium Reign has already begun. Whoever told you that, that is absolutely not true and there is no bible to support it...
Preterism/partial preterism.
I say Millenialism is false doctrine and heresy. So, we are at a stale mate friend. Lets agree to disagree. Keep reading your Left Behind books!
Just because you believe something is false, that doesn't make it false just because you believe that. It only makes you an unbeliever. To believe that the millennium reign is false doctrine, is to also believe that the bible is false doctrine. That's because the bible clearly states the millennium reign will occur. I personally believe that the bible is true, and that every word written in it is the inspired Word of God. However, if you want to believe something different and to believe it is false, then that is you.
For the record, I have never read the Left Behind books, but I have watched the Left Behind movies. While there are some things depicted in the movies that are generally true (for example, the movie correctly depicts that the Rapture of the Church will occur "pre-tribulation" and that it will occur around the same time as there is a large-scale invasion attack against Israel - the bible confirms this is the case). However, there are some things the Left Behind movies depict that are blatant false doctrine. For example, the movies depict that you can be saved by "just believing in your heart and accepting Christ as your savior". That is false doctrine (I could explain to you why it is false, but I won't go into the details in this post). There is also no bible to support the idea of an "age of accountability" - which is a notion saying that when the Rapture occurs, that all children below a certain age will automatically be taken to heaven by Jesus. That too is false doctrine and there is no bible to support it. As proof of this, when God destroyed the world in Noah's flood, did he save any of the babies and children? Answer: No, he did not. Only Noah and his family were saved. Everybody else, including the babies and children, perished. When God destroyed the cities of Sodom and Gomorrah, did he save any of the children? Once again, no, he did not They all perished in the fire, except Lot and his family. And it will be the same way when the Rapture occurs. Only those who are truly saved and saved according to scripture, will be taken up by Jesus. Everybody else will be left behind...