This is not a question with a simple answer. First, it must be stated that there is no historical evidence whatsoever (and no historical accounts outside of the Bible and the associated non-canonical early Christian literature) to support the notion that Jesus ever performed any miracles, was resurrected, or any of the other events that are claimed by Christianity (at least, not from the first century CE.)
This doesn't mean that none of it occurred, but it does mean that if the miracles did occur, they would be very difficult to establish. It's not even entirely known if Jesus ever existed, and certainly, if he did exist, he would not have had the Roman name "Jesus". Instead, he would likely have identified himself under the Hebrew name "Yeshua ben Yosef", which translates into modern English as "Joshua, son of Joseph" (this is still the name used by Messianic Jews.) In Islam, Jesus is identified as Isa (or Yasu), a name that harkens back to its earlier roots.
The earliest accounts that we have of Jesus come from Paul, the author of Romans and Galatians (and supposedly some other Biblical works as well, but that attribution is controversial amongst historians.) As far as confirmed authorship is concerned, it's clear that Paul was writing, at the earliest, around 20 years after the death of Jesus. It's unclear if Paul actually knew Jesus himself, although he tries to establish in his writings that he did. I have no reason not to believe him, but neither do I really have reason to believe what he has to say either. For that reason, we should look to independent verification and to the broader culture in which he lived.
First, we can ask why was Christianity historically successful? Why is it that around a third of the world's present population self identifies as Christian? How did this small Jewish cult become the single largest religion in the world today?
The early success of Christianity was due in large part to certain reforms that Paul argued for. Christianity began its life as a first century apocalyptic Jewish cult. Judaism in the first century CE was very difficult to join, and correspondingly very difficult to spread. Membership in Judaism was only achieved after a long conversion process, accompanied with various rituals. One had to be circumcised (most gentiles of the period were not) and one had to obey the various Jewish laws as they were then laid down in the Septuagint (the early form of the Hebrew Bible which was in common use at the time.) Paul argued for the establishment of gentile Christian churches, membership in which did not entail circumcision or long drawn out rituals. He also argued on the topic of the application of Jewish law to the gentiles. Christians, in the modern world, find his words to be central to their beliefs.
Unlike Judaism or many other religions in the first century, Christianity was not an exclusive club. The early Christians went to great effort to appeal to the commoner, the poor, and the disenfranchised. Other contemporaneous religions, particularly the Greek mystery cults, had elaborate feats that one had to accomplish in order to gain membership. Often, this meant that religions functioned as an elite social club which could be joined only by those who went through elaborate, strenuous, and sometimes painful initiation rituals.
Other religions, particularly folk religions, did have members from the common masses, but it would have been virtually unheard of to proselytize specifically to the poor. Early Christianity rejected this notion of religious orthodoxy, and sought converts specifically amongst the lower social and economic classes. Initially, it spread from the bottom up instead of from the top down.
There is a useful comparison that can be made here between Christianity and a number of other religions from the same time period. Mithraism is thought to have been the primary competitor of Christianity in the first century CE. It concerns a Christ-like being known as Mithras, about whom only scant references survive (though Mithraic temples are abundant.)
It is known that he was believed to have been divinely born out of rock, and to have wrestled with a bull (with 700 out of the 1000 known Mithras inscriptions related to bull-killing.) The religion was popular amongst the military. Additionally, in the third century, there appears to have been a revival of paganism amongst Roman bureaucrats which prominently featured Mithraism.
Early Christian religions and Mithrain rituals deeply resembled each other, so much so that the early Christians were eager to demonize Mithraism as a demonic copy of Christianity. Tertullian remarked on the Mithraic rituals as including something akin to baptism, calling it a "diabolical counterfeit" of Christian ritual. 19th century scholar Marvin Meyer remarked that had history unfolded differently, we might be living with a Mithraic majority today.
Nonetheless, by the 4rth century, Mithraism had essentially died out in what remained of the Roman Empire. With the Emperor Constantine converted to Christianity, and religion becoming the focal point of the Empire with the associated loss of religious freedom, Mithraism was basically eradicated (along with all other competitors to Christianity.) In this later period, there were severe penalties for not being Christian, often including death or torture. Thus,the survival of Christianity after the successful incorporation of the religion into the government is not altogether surprising. In fact, it's more surprising that some of the competitors did survive the Medieval period (particularly the late Medieval period.)
Besides, Mithraism was not proselytized to the masses. It was usually proselytized in the Roman army; but with the dissolution of the Roman army with the fall of the Empire, the base of new converts was de-stabilized. Correspondingly, Mithraism disappeared altogether.
But given the robustness of Christianity due both to its early proselytization methods and later identification with the nation-state, we are left with the question of how this whole thing got started in the first place.
Christians will, of course, answer that Jesus was the messiah, and that it got started due to people witnessing the event. I will attempt to show that we can explain the origins of Christianity without positing anything of that sort.
First, it needs to be understood that Christianity is not unique in claiming a fantastical foundational story replete with miraculous events and supernatural interventions.
Mithraism similarly concerns an individual who was in some sense divine.
The Quran was supposedly delivered to Mohammed by the angel Gabriel.
Mormans believe that the Book of Mormon was delivered, on golden tablets, to Joseph Smith by the angel Moroni.
Buddhism tells us that Siddhartha Guatama reached spiritual enlightenment underneath the Bodhi tree, and that he was tempted to leave the tree by supernatural forces.
The Aztec believe their ancestors were guided by Huitzilopochtli to found a city at a place where they would see an eagle perched on a fruit-bearing nopal cactus. Aztec mythology states that the city of Tenochtitlan was founded on that site. The scene is depicted on the Mexican flag.
In many of these religions, people are reported to have had supernatural visitations and to have died for their beliefs. Joseph Smith was shot while imprisoned by a group of people who were against Mormonism. Members of the Church of Latter Day Saints view Smith as a martyr.
Most people would regard most of these establishment stories as untrue. Even those who regard one of them as true most likely do not regard all of them as true. However, in each one, members of the religion can say things such as:
Mithraist: "If Mithras didn't exist, how did Mithraism start?"
Muslim: "If Mohammed was never visited by an angel, and was so illiterate that he couldn't write the Quran himself, where did the Quran come from?"
Mormon: "If the angel Moroni never visited Joseph Smith, why did he die for a lie and where did the Book of Mormon come from?"
Buddhism: "If the Buddha was never enlightened under the Bodhi tree, why did people follow his teachings?"
Aztecs: "If Huitzilopochtli never led our ancestors, the wanderers, to the Eagle, where did the city of Tenochtitlan come from?"
These are to be compared to the Christian version of the question:
"If Jesus had never been resurrected, where did Christianity come from?"
While there is some contention as to whether or not there ever was such a person as Jesus, I think it is most likely that the story is inspired by either one individual or an amalgam of various individuals. Radical rabbis who self-identified as the messiah were not uncommon in the first century CE, nor was it uncommon to find political figures who identified themselves as having divine origins in the Hellenistic world more generally. Even the virgin birth was an element that figured in the supposed ancestory of most Roman emporers. For instance, emporer Augustus was said to have been born of a virgin. In fact, the entire line of Caesars were believed to have had divine origins. Others both in the Hellenistic world and elsewhere were said to have been the product of the coupling between a god and a mortal woman.
I think it to be likely, though it is is difficult to establish, that Jesus was a radical rabbi and possibly one who proclaimed himself to be of divine nature or was proclaimed thusly by his followers. It should be noted that it is unlikely he proclaimed himself to be God; trinitarian theology appears to have been a later developed (most likely sometime in the 3rd century CE, and possibly at the Council of Nicaea.) Like most of the founders of the world's religions, his followers would have told successively more exaggerated stories about him. A nice parallel occurs in Buddhism, where, despite proclaiming that he was not a god nor divine on several occasions, Buddhist literature and art developed quite a fantastical supernatural depiction of his nature. He was said to have glowing, golden skin, and to be absolutely beautiful to behold (thus explaining the golden statues of the Buddha that figure prominently in Buddhism throughout the world. In Thailand, the Reclining Buddha depiction, in the temple Wat Pho, is probably one of the most magnificent depictions in this series. The Reclining Buddha is one of the largest depictions of the Buddha in the world.)
Despite the fact that he is depicted as proclaiming that he detested, rejected, and despised miraculous claims, there are a plethora of miracles the Buddha is said to have performed. Quite likely, if the Buddha ever existed, he did not perform miracles nor claimed to; these were most likely added as later embellishments.
It is known that certain parts of the Jesus story were stolen from other sources. After Jesus is born, it is said in several places that Mary, Joseph, and the baby Jesus fled to Egypt as the emporer ordered the killing of all new born babies. This story is stolen directly from Exodus, and probably was meant originally to tie Jesus to Moses. Nonetheless, this motif of Jesus-as-Moses is most likely entirely fictional.
Several scholars have advanced the claim that early Christianity was likely a syncretic religion; i.e. a combination of a number of early and pre-existing religions. To some limited extent, this is undoubtedly the case; that there are certain archetypes or narrative themes, as well as ritual practices, that early Christianity borrowed from other sources is undeniable (it's commonly known, for example, that the various Christian holidays are directly stolen from older pagan traditions.) How heavily early Christianity was syncretic is a hotly debated topic.
It should be said that the theme of a deity who dies and is reborn is something which appears in many of the world's religions. Stories with this archetype are documented amongst the Australian aborigines, the Akkadians, the ancient Arabians, the Aztec, the Canaanites, the Dracian culture, the ancient Egyptians, the Etruscans, the ancient Greeks, the Hindus, Japanese traditional culture, the Khoikhoi, the Chochenyo, the Norse (Vikings), ancient Romans, the Slavs, the Sumerians, and the Yoruba. There are others, but suffice it to say that this is a common mythological theme.
Herodotus wrote of a being called Zalmoxus, who was believed to have died and been reborn. It was believed that if one followed Zalmoxus, one would be given eternal life. On this topic, Richard Carrier writes:
"Then there is Herodotus, who was always a popular author and had been for centuries. He told of a Thracian religion that began with the physical resurrection of a man called Zalmoxus, who then started a cult in which it was taught that believers went to heaven when they died. We also know that circulating in the Middle East were very ancient legends regarding the resurrection of the goddess Inanna (also known as Ishtar), who was crucified in the underworld, then rescued and raised back to earth by her divine attendant, a tale recounted in a four thousand year old clay tablet from Sumeria. Finally, Plutarch writes in the latter half of the 1st century how 'Romeo-and-Juliet-style' returns from the dead were a popular theme in contemporary theatre, and we know from surviving summaries and fragments that they were also a feature in romance novels of that day. This trend is discussed at some length in G. W. Bowersock's book Fiction as History."
There are known cultural mechanisms by which stories like the Resurrection are created and then take firm hold. The extravagant embellishment or blatant mythologization of cultural heroes and past kings was a tremendously common theme throughout history. Even the idea that a fallen king or cultural hero will some day return is a common re-occuring story. The legend of King Arthur was likely inspired by an actual person. However, the only writings we have about him indicate that he will eventually return from hiding and a better era will come to pass. Even in today's society, the return of a fallen hero is psychologically appealing; think of Elvis Presley or Tupac Shakur. Googling "Tupac isn't dead" conjures up almost 10 million hits as of this writing. "Evis is alive" brings up nearly 2 million.
In fact, the idea that Tupac isn't dead has spawned a growing body of hoaxes. A fake CNN article was posted online in April 2005 claiming that the musician was alive and well. The image of the CNN article has been widely circulated, but it was originally posted as an April Fool's Day joke. The original site has been forcibly removed by CNN, but the image continues to spread. Depending on how effectively this meme makes its way through the internet, perhaps future generations will proclaim that "Tupac has Risen" and that "Tupac is Lord".