Short answers, pulled from the story.
The Roman Republic began in 509 BC when the Senate expelled Tarquin the Proud after his son Sextus raped Lucretia. Lucius Junius Brutus led a revolt that established two consuls elected annually to check each other's power.
Plebeians emerged as a distinct group in 494 BC when they withdrew labor during a famine while wealthy patrician families controlled all high offices. Gaius Licinius Stolo and Lucius Sextius Lateranus pushed legislation in 367 BC opening the consulship to plebeians, and Quintus Hortensius passed the lex Hortensia around 287 BC making plebiscites binding on all citizens.
Rome built one hundred quinqueremes in two months after capturing a Carthaginian ship in 260 BC and used the corvus grappling engine to board enemy ships at Mylae. Hannibal crossed the Alps with thirty-seven elephants in May 218 BC but Scipio Africanus won the Battle of Zama against him in 204 BC before Rome destroyed Carthage completely in 146 BC.
Eunus and Cleon led slaves in Sicily during the First Servile War from 138 to 132 BC until Marcus Perperna and Publius Rupilius crushed this uprising. Spartacus led seventy thousand men in the Third Servile War starting in 73 BC before M. Licinius Crassus defeated these rebels.
Senators led by Cassius and Brutus assassinated Caesar on the 15th of March 44 BC after he held both dictatorship and tribunate powers. Mark Antony formed an alliance with Octavian and Lepidus known as the Second Triumvirate which defeated conspirators at Philippi in 42 BC.
By 27 BC the Senate granted Octavian special powers including sole authority within Rome and he received the name Augustus marking the end of the Republic. This transformation occurred without formal constitutional changes despite centuries of evolution from unwritten guidelines passed down through precedent.