Title: Empire
Content:  Another theory blames the rise of Christianity as the cause, arguing that the spread of certain Christian ideals caused internal weakness of the military and state. In the book The Fall of the Roman Empire, by Peter Heather, he contends that there are many factors, including issues of money and manpower, which produce military limitations and culminate in the Roman army's inability to effectively repel invading barbarians at the frontier. The Western Roman economy was already stretched to its limit in the 4th and 5th Centuries C.E. due to continual conflict and loss of territory which, in turn, generated loss of revenue from the tax base. 
Title: Greco-Roman relations in classical antiquity
Content:  the native Romans began to migrate to more prosperous areas in the east Hellenized over time, the rest of the Romans in Italy had to face looting very frequently. Depending only on militias armed by the upper classes, trade routes in the West were almost non-existent due to the insecurity of the routes, this plus different key factors such as the frequent use of barbarians in the Roman army over time would lead to the fall of Rome in 476 after much looting in Rome itself and the Italian peninsula. The effects of the Fall of the Western Roman Empire for the 
Title: Western world
Content:  ended. Conquest was enforced using the Roman legions and then through cultural assimilation by eventual recognition of some form of Roman citizenship's privileges. Nonetheless, despite its great legacy, a number of factors led to the eventual decline and ultimately fall of the Roman Empire. The Roman Empire succeeded the approximately 500-year-old Roman Republic (c. undefined 510 BC – 30 BC). In 350 years, from the successful and deadliest war with the Phoenicians began in 218 BC to the rule of Emperor Hadrian by AD 117, Ancient Rome expanded up to twenty-five times its area. The same time passed before its 
Title: Proto-globalization
Content:  became cities with structures designed by the best Roman architects, which hastened the spread of Rome's "modern" way of life while absorbing the traditions and beliefs of these native cultures. Nationalist ideology as well as propaganda supporting the Roman Army and military success, bravery, and valor also strengthened the Roman Empire's spread across Western Europe and the Mediterranean Area. The Roman Empire's well-built aqueducts and cities and sturdy, effective naval fleets, ships and an organized system of paved roads also facilitated fast, easy travel and better networking and trade with neighboring nations and the provinces. During the Han dynasty under Han Wudi (141–87 BCE), the Chinese government united and became powerful enough that China 
Title: History of Europe
Content:  Roman Empire centred in Ravenna, and the Eastern Roman Empire (later to be referred to as the Byzantine Empire) centred in Constantinople. The Roman Empire was repeatedly attacked by Hunnic, Germanic, Slavic and other "barbarian" tribes (see: Migration Period), and in 476 finally the Western part fell to the Heruli chieftain Odoacer.  Roman authority in the Western part of the empire had collapsed, and a power vacuum left in the wake of this collapse; the central organization, institutions, laws and power of Rome had broken down, resulting in many areas being open to invasion by migrating tribes. Over time, feudalism and manorialism arose, two interlocking institutions that provided for division of 
Title: Migration Period
Content:  crossing of the Rhine was made by a group of Vandals, Alans and Suebi. As central power broke down in the Western Roman Empire, the military became more important but was itself now dominated by men of barbarian origin. There are contradictory opinions as to whether the fall of the Western Roman Empire was a result of an increase in migrations, or both the breakdown of central power and the increased importance of non-Romans were the result of internal Roman factors. Migrations, and the use of non-Romans in the military, were known in the periods before and after, and the Eastern Roman Empire adapted and continued 
Title: Human history
Content:  breeding of horses strong enough to carry a fully armed archer made the nomads a constant threat to the more settled civilizations. The gradual break-up of the Roman Empire, spanning several centuries after the 2nd century CE, coincided with the spread of Christianity outward from the Middle East. The Western Roman Empire fell under the domination of Germanic tribes in the 5th century, and these polities gradually developed into a number of warring states, all associated in one way or another with the Catholic Church. The remaining part of the Roman Empire, in the eastern Mediterranean, continued as what came to be called the Byzantine Empire. Centuries later, a limited unity would be restored to western Europe through 
Title: Colonization
Content:  The decline and collapse of the Roman Empire saw (and was partly caused by) the large-scale movement of people in Eastern Europe and Asia. This is largely seen as beginning with nomadic horsemen from Asia (specifically the Huns) moving into the richer pasture land to the west, thus forcing the local people there to move further west and so on until eventually the Goths were forced to cross into the Roman Empire, resulting in continuous war with Rome which played a major role in the fall of the Roman Empire. During this period there were large-scale movements of peoples establishing new colonies all over western Europe. The events of this time saw the development of many of the modern-day nations of Europe like the Franks in France and Germany and the Anglo-Saxons in England. 
Title: Barbarian kingdoms
Content:  The rise of the barbarian kingdoms in the territory previously governed by the Western Roman Empire was a gradual, complex and largely unintentional process. The starting point of the process that led to their formation were the migrations of large numbers of barbarian (i.e. non-Roman) peoples into the territory of the Roman Empire. The migrations were spurred by both invasions and invitations. Inviting peoples from beyond the imperial frontier to settle Roman territory was not a new policy, but something that had been done several times by emperors in the past, mostly for economic, agricultural or military purposes. The capacity for immigration in 
Title: Sack of Rome (410)
Content:  went on to become foundational to Christian thought. The sack was a culmination of many terminal problems facing the Western Roman Empire. Domestic rebellions and usurpations weakened the Empire in the face of external invasions. These factors would permanently harm the stability of the Roman Empire in the west. The Roman army meanwhile became increasingly barbarian and disloyal to the Empire. A more severe sack of Rome by the Vandals followed in 455, and the Western Roman Empire finally collapsed in 476 when the Germanic Odovacer removed the last Western Roman Emperor, Romulus Augustulus, and declared himself King of Italy.

Question: what factors led to the rise of the roman empire?
Answer: Ulpian.