This almost never happens. Conquered men, women, children, elderly people -- they don't spontaneously rise up and try to kill people who abuse and oppress them.
I'm not saying that the rebels automatically win. I'm just saying that the revolts and uprisings WILL occur. Using Rome itself as an example (http://www.musesrealm.net/rome/timeline.html and http://en.wikipedia.org/wiki/List_of_revolutions_and_rebellions):
340-337 B.C. - Revolt and end of the Latin League
147–139 BC: The Lusitanian Rebellion against the Roman forces in modern day Portugal, led by Lusitanian leader named Viriathus.
135-132 B.C. - Slave Rebellion in Sicily
103-102 B.C. - Second Sicilian Slave Rebellion
91-88 B.C. - Rome goes through a civil war
82 B.C. - Rome enters another civil war; Sulla becomes dictator and restores the power of the Senate
73-71 B.C.- Sparticus leads a revolt of slaves and gladiators and is killed along with most of his followers
52–51 BC: The revolt of the Celtic Gauls, led by Vercingetorix, was crushed by Julius Caesar.
49–45 BC: Julius Caesar crossed the river Rubicon heading part of the Roman army and marched on Rome. After overthrowing and assuming control of Pompeian government, he was proclaimed "dictator in perpetuity".
6–9 A.D.: The Pannonians, with the Dalmatians and other Illyrian tribes, revolted against the Roman Empire, and were overcome by Tiberius and Germanicus, after a hard-fought campaign which lasted for three years.
9 A.D.: The Arminius revolt against the Roman Empire; alliance of Germanic tribes led by Arminius ambushed and annihilated three Roman legions led by Publius Quinctilius Varus in the Battle of the Teutoburg Forest.
60–61 A.D.: Boudica, queen of the Celtic Iceni people of Norfolk in Roman-occupied Britain, led a major uprising of the Briton tribes against the occupying forces of the Roman Empire
66–70 A.D.: The Great Jewish Revolt, the first of three Jewish-Roman wars that took place in Iudaea Province against the Roman Empire
69–70 A.D.: The Batavian rebellion in the Roman province of Germania Inferior.
115–117 A.D.: The Kitos War, the second of the Jewish-Roman wars.
132–135 A.D.: Bar Kokhba's revolt, the third and last of the Jewish-Roman wars.
286 A.D.: Rebels in Gaul, known as Bagaudae, are crushed by the Caesar Maximian and his subordinate Carausius, working for Augustus Diocletian.
532 A.D.: The Nika revolt in Constantinople.
This is by no means a comprehensive list. Pretty much every nation or empire has experienced revolts and rebellions. Pretty much every nation that has had
large-scale slavery has had Slave Revolts. All it takes is for the oppressed to start thinking that the attention of their masters is elsewhere, or "What have we got to lose?" (in the case of particularly harsh slavery).