Question: Will the thousand-year reign occur immediately after the Great Tribulation?
Yes; that is my understanding.
The Millennial Period
There is, as said, clearly a reason, or more correctly many reasons for this special period of time (1000 years, Rev. 20:1-5). It is inescapable to the notice that the statement is linked to Satan and his binding; and therefore an inextricable link to God’s eventual purposes and love for human kind, (Jn. 3:16). It also cannot escape notice that God’s power is shown in the imprisonment of Satan for this future period, whereas he had been free to act to his advantage in Eden! By virtue of Satan’s inability to act as he did with Eve in Eden, a great force for untruth and therefore action in untruth is removed from people’s behaviour, and therefore Satan cannot be blamed in the Millennial for human behaviour, as was the case in Eden and in many cases now! See: Eve and Adam. However, sin (the fallen state) is still in human nature, which will still generate the desire to sin, and resist the Will and holiness of God; and is still linked to the knowledge of good and evil! The major differences of that period and now, are that nobody will be in any doubt as to the existence of God and His Christ (Messiah); Satan has no influence on human behaviour; so that rebellion against the Godhead, sinning by the person, will all be attributable to the person and their knowledge of good and evil! Justice against the sinner will be swift and decisive, from the Godhead in Jerusalem. There are clearly reasons for this 1000 year period.
There are two groups of people being dealt with by God and His Christ at that time; Jews and Gentiles (the Nations), with the Jews first again (Ammi)!