@Nkrumah Was Right - here the long answer:
This is the generally agreed timeline:
25-30 AD: Jesus teaches the disciples
30 AD: Jesus is killed
30-50 AD: Disciples become the leaders of the church and develop Jesus's teachings into a practical theology and communal way of life, with very little influence from Paul. Christianity spreads to Jordan, Syria, Lebanon, Egypt, Ethiopia, Turkey, Greece, Italy, and possibly even India, long before Paul had been known in any of those places.
mid-30s AD: Paul becomes a follower of Jesus
late-30s AD: Paul visits Jerusalem and meets the original disciples for first time, but only briefly and as a new believer.
late-30s to mid-40s: Paul preaches in Tarsus, guiding people towards Jesus, but is not in a major Christian center and doesn't appear to be in a leadership position.
late 40s: Paul is invited to begin working in Antioch and appears to be treated as a significant leader in the church for the first time
50 AD: Paul attends the council in Jerusalem. His position is treated with respect and he is clearly an important figure in the church, but he is not seen as any more important than any other leader there.
50s AD: Paul begins to preach more widely, going on his "missionary journeys" across Syria, Turkey, Greece, and Italy, and writing letters to many churches. In most of these places, he is supporting already established churches rather than creating his own. The only places he seems to spend extended time (other than Antioch) are 2-3 years each in Corinth and Ephesus, neither of which are major Christian centers.
61-63 AD: Paul visits Rome for first time, is imprisoned, then acquitted and leaves
64 AD: Rome burns. Nero blames the Christians for it in order to scapegoat them and fuel widespread persecution. This shows that the Christian faith had already grown so large, far outside of Jerusalem, that the emperor was taking notice and thought they were a problem he had to deal with violently.
Let's stop there for a moment. At this point, the church has been building for 35 years, spread over nearly the entire Roman world, yet Paul hasn't appeared to be driving practice or theology outside of perhaps Antioch and the relatively small Christian communities he has a special relationship with. Even the places where he visited and wrote letters once or twice, do you really think a church established by the disciples of Jesus himself is going to change their beliefs and leave the faith based on a couple short visits or 1-2 letters from some other guy? No one does that. There's simply zero evidence that Paul had somehow eliminated the beliefs of an entire international Church, or that he was opposed to the teachings of the apostles in any way except for the disagreements in how to treat Gentile converts. Every indication is that Paul fit fluidly into the church beliefs.
66-70 AD: Jewish war begins, the temple is destroyed, Jews and Jewish Christians are scattered, many fleeing to Jordan. Christianity spreads to Armenia as well and grows rapidly.
68 AD: After another journey through Europe, Paul is executed by Nero in Rome
60-70 AD: The gospel of Mark is written. It uses preexisting oral stories about Jesus as taught by the apostles, but the author doesn't even appear aware of Paul's letters.
65-75 AD: Letter of James written, showing church development in Jerusalem in line with the teachings of Jesus, with no obvious influence from Paul
~75 AD: The Syrian stoic Mara bar Serapion writes of Jesus's execution, showing that the details of Jesus's story are known in the non-Christian world
89 AD: Christianity is established in modern-day France
70-90 AD: Gospel of Matthew is written. Appears to use Mark as well as other oral stories of Jesus told in church, but author was either unaware of Paul's letters or don't think his perspective is relevant to this task.
70-90 AD: Luke and Acts are written by Luke, a former traveling companion of Paul. The books show extensive knowledge of Paul's life all the way up to his death in Rome, yet still prioritize the stories and theology of Jesus. There is no indication that Luke knows the theological details of Paul's letters, only his life story and the travels they engaged in together.
93 AD: Jewish historian Josephus makes multiple references to Jesus in his writings, including his death and claimed resurrection, showing again how important Christianity had become to the non-Christian world.
98 AD: Emperor Neva issues an official decree that Christians are distinct from the tax on Jews, showing again that they were large enough to warrant attention from the Emperor AND their distinctness from Judaism is already noticed.
100 AD: Christianity has spread to Monaco, Algeria, Iraq, and Sri Lanka. At this point in time, we know of at least 40 different cities across the Roman Empire that had an active Christian community
90-110 AD: Gospel of John, Revelations, and the 1st/2nd letters of John are written by an author from the "Johnnian community". These books show new theological developments quite seperate from those of Paul.
Somewhere around this time, early Christian documents including the Didache, Epistle of Barnabas, Exposition of the Sayings of the Lord, and Shepherd of Hermas were also written. They remained popular for hundreds of years of Christian history. They show deep knowledge of Jesus's life, but don't rely on Pauline theology. The letters of Papias of Hierapolis, a bishop of Turkey around 100-110 AD, state that he had learnt the teachings of Jesus in his youth from those who knew Jesus personally. So 60+ years after Jesus's death, his teachings are still clearly the focus of church life and having a personal connection to the apostles is seen as important.
90-110 AD: Paul's individual letters begin to circle around the larger churches. Soon some congregations end up reading them aloud like Gospel passages. The First Epistle of Clement, a letter from the bishop of Rome to the church in Corinth, refers to both the teachings of Jesus and the letters of Paul, and sees both as important. The seven letters of Ignatius, a bishop of Antioch who wrote between 98 AD and 117 AD, also show knowledge of Paul's letters.
~110 AD: Second Peter is dated to here, in part because it is the only Biblical book outside of Paul's writings which demonstrates knowledge of the contents of Paul's letters.
112 AD: A letter from Pliny the Younger to the Emperor Trajan discusses the issue of how Christians should be persecuted.
116 AD: Roman historian Tacitus refers to Christians, staying that Nero blamed the fire of 64 on them.
125 AD: The date of a fragment of the book of John written in Coptic that was found in Egypt. Historians assume that by now, all of the Biblical books were circulating widely in the church from Spain to Egypt and everywhere between.
155 AD: The bishop Polycarp is martyred for refusing to worship the emperor. In his statement regarding the charges, he declares that he has been a Christian his 86 years of life and was originally a student of John the apostle (Polycarp would have been a student in the 80s, church history suggests the apostle John died around 100 AD). He is the last living person to have had contact with an apostle. Polycarp quotes from Matthew, Acts, 1 John, Philippians, Jude, 1 Peter, 1 Timothy, 2 Timothy, and Romans.
This is proof that in 155 AD, over a century after Jesus's death, someone who has known one of the apostles was still alive and had no problem fully integrating the Gospels with the letters of Paul.
There's simply zero historical evidence for claiming that the teachings of Paul were separate from the church of the apostles, or that Christianity was some fringe thing outside of Paul.