The Roman Empire began as the Roman Republic in 500 BC. The rich people of the Republic no longer wanted to be ruled by Etruscan kings. By promising the poor people power, together they were able to overthrow the kings. By 274 BC, the Romans had conquered all of Italy. They were so powerful that when Sicily was in trouble, they turned to the Romans for help. The Carthaginians, who lived in parts of Sicily, feared that the Romans would try to conquer them, so when the Romans arrived, the Carthaginians attacked. This began the Punic Wars in 264 BC, which lasted until 146 BC. Following the Punic Wars, many different emperors ruled, and many civil wars were fought within the Empire. These wars began in 135 BC and lasted until 30 BC. They were mostly fought over the topic of succession to the throne, since there were multiple heirs, of which almost all claimed to be the legitimate heir.
The most influential emperor of this time was Julius Caesar, who was actually part of the first triumvirate in 49 BC. Exiled out of fear after one of the other leaders died, he returned as an outlaw and general, invading the city and declaring himself emperor. He was assassinated in 44 by the Senate, who had become fearful of his dictatorship. Soon afterwards, another Triumvirate was formed, made of Mark Antony, Augustus Caesar, and Lepidus. Lepidus died, and Mark Antony and Augustus battled for control, with Augustus as the victor. Augustus was followed by "Bad Emperors". A few good emperors came afterwards, but they could not reverse the decay of the Empire. The Western Roman Empire is generally accepted to have ended in 476 AD. The Eastern Roman Empire, however, persevered and reemerged as the Byzantine Empire.
All roman citizens in the republic could gather in periodic assemblies. These gatherings were to elect various magistrates, some of whom were specifically entrusted with the task of representing the common people. The most important legislative body was the Senate, mainly composed of aristocrats.
Tax collection became increasingly difficult as the people of the empire fell on hard times. The decline of Rome was more disruptive than the collapse of the classical dynasties in Asia. After about 180 CE, political confusion and many disputes over succession produced a series of weak emperors. The measles and other contagious diseases decreased the population from almost a million to 250,000 people. The decline of the population added to the trouble of recruiting armies which created even more trouble for the people since they now could not be very well defended from the invading "Barbarians" (anybody that wasn't Roman and didn't speak Latin) that frequently raided towns, cities, and villages.