The Roman Republic, widely-known as among the first semi-democracies in the world, lasted for more than 450 years and was considered the basis for many forms of modern republican governments across the world. The Republic ended in 27 BC with the enthronement of Octavian as Augustus following bitter post-Ceasar civil wars. Following by the popular rule of Augustus were two infamous Emperors, Tiberius and Caligula. The later, known as the Mad Emperor of Rome, was assassinated and succeeded by his nephew and then-Consul Claudius in 41 AD. The assassination of Caligula was originally planned by the Senate to re-establish the Republic, but their underestimation of Claudius gave him the opportunity to succeed Caligula as Emperor of Rome instead of following the Senate's plan.
In this timeline, the Senate managed to keep Consul Claudius to follow their plan and successfully restored the Republic.
The first centuries of this Second Republic saw a period of increasing distribution of power to the mass, with the citizens of Rome's client states and allies finally given suffrage in 120 AD following the Second Social War. With the increasing membership, the Roman Assemblies became much more powerful and ultimately removed the Senate's power to vet candidates for public offices in 205 AD, effectively replacing the oligarchy with a representative democracy. However, this also kindled the rise of populism and demagogy of Roman politics. With a low literacy rate and the lack of education spending, the Roman citizens elected a new generation of incompetent officials that undermined the Republic's stability.
With the bitter defeat of Rome in the Battle of Abritus in 231 during the Roman-Gothic War, Rome lost the provinces of Dacia and Moesia to the Gothic and Scythian tribesmen. Consul Decius and three Roman legions were killed by the Gothics, prompting Gallus as the most senior Senator to assume the Dictatorship of the Republic. After his victory in 233, the Senate proclaimed him as the Emperor of the Romans, effectively ending the Second Republic and establishing the Second Empire. Despite this, the seed of democracy still propeled within Rome as evident by the continuation of local elections until the 14th century.