The idea of 6000 years of history followed by 1000 years of an earthly "messianic kingdom" was a long-held Rabbinic doctrine even before the advent of Christianity. This doctrine of a 7-thousand year history of the world, referred to by historians as Jewish "messianism," was brought into the early Christian church by some of the early believers.
Rabbinic Messianism was originally called "chiliasm" from the Greek word "chilioi" meaning "a thousand," but later became known as "millennialism" after the word "mille" which is Latin meaning "a thousand." Chiliasm/Millennialism was only one of the various views held by early Christians. There actually was little or no consensus on doctrine in these earliest years, and you will find various forms of eschatology were being discussed and written about, which is why you will find some students today quoting one early Christian to support their view while others will quote another early Christian to support a completely different view.
To understand these earliest years, it is helpful to go back to the very beginning of the church and the Scriptures. Very early on, a dispute came about between what is referred to as the "Pauline" and the "Petrine" schools of thought, which at heart was a struggle between the Gospel (Pauline) and the Law (Petrine). This struggle is evidenced by the disagreement in A.D. 48 between Paul and Peter (ergo the "Pauline" and "Petrine" terms) recorded in Galatians 2:11-21. This dispute was the cause of the first Christian council held at Jerusalem that same year, recorded in Acts 15.
But this council and its decision did not end the tension between the Pauline and the Petrine factions and the struggle continued even into the fourth century when the dispute about when Easter should be observed finally came to a head, some holding that Easter should be observed on the 3rd day after the 14th day (Passover) of the Jewish calendar, regardless of what day of the week that 3rd day should occur, and others holding that Easter was the observance of the resurrection and should be observed on the Sunday following the Passover, regardless of the date on the calendar that Sunday fell on. This difference caused a breakdown in fellowship because while one church was feasting in celebration of the Resurrection, another church was still fasting in observance of the Crucifixion, making fellowship between these churches impossible during this time.
This dispute was finally settled when a council was convened, and every head of every church throughout the world came together to discuss the issue and make a decision, the Council of Nicea in A.D. 325. The decision was that "Easter" (at the time it was called the "feast of the resurrection") should be observed on the first Sunday following the paschal moon, that is, the moon of Passover (the first full moon nearest the spring equinox), which is when the Biblical feast of Passover was observed, and the following Sunday being the day on which Jesus historically rose from the dead and which, for that reason, was held sacred by Christians the world over and the day on which the church since the days of the Apostles had come together as a body for study, worship, and fellowship.
But again, this early decision of the worldwide body of Christ did not emphatically settle matters, and even to this day, there are Petrine factions within the church who claim that Christians must be obedient to the Law of Moses. The orthodox Christian view, however, is that salvation is by faith without the works of the Law, but that the fruit of the spirit in the life of the Christian is an obedience that transcends compliance to the commandments of Moses and manifests the very spirit of everything that is good and just and holy.