Short answers, pulled from the story.
The Constitution of the Roman Republic had three main branches: the Assemblies, which held supreme political power and elected magistrates; the Senate, which advised magistrates primarily through custom and influence rather than legal authority; and the magistrates, elected by the people to govern the republic with religious, military, and judicial powers.
The collapse of republican government and norms began in 133 BC. The process accelerated through civil wars and constitutional crises, with Caesar's civil war starting in 49 BC as one suggested endpoint. The lex Titia in 43 BC created the triumvirate, and the transformation was complete with the emperor Tiberius' successful accession in AD 14.
The senatus consultum ultimum, or final decree of the senate, was a resolution advising magistrates to use force to suppress domestic uprisings. First used in 121 BC against Gaius Gracchus and Marcus Fulvius Flaccus, it granted no legal authority or immunity but provided political cover for magistrates who acted outside the law. Its use was hotly debated throughout the late republic.
The Conflict of the Orders was a prolonged political struggle between the patricians and plebeians in the early republic. Key events included the plebeian secession to the mons Sacer in 494 BC, which forced recognition of the plebeian tribunate, and the passage of the Licinio-Sextian rogations in 367 BC, which allowed plebeians to stand for the consulship. The conflict formally ended in 287 BC when the lex Hortensia gave plebiscites the force of law for all Romans.
Roman citizens were organised into three types of voting units: curiae, centuries, and tribes. Each unit cast a single collective vote based on the majority of its individual members. Elections were decided not by total individual votes but by which candidate first secured approval from a majority of voting blocs. All votes had to be completed within a single day.
Sulla expanded the senate from around 300 members to over 500, created law codes enforced by expanded permanent courts, required senate approval of all bills before the assemblies could vote, restricted the tribunician veto to individual clemency requests, and barred men elected tribune from holding any other magistracy. By 70 BC, the consuls Pompey and Crassus had reversed the restrictions on tribunician powers.