What event caused the etruscans and the Romans to finally fight?

Answer 1

The Etruscans and Romans did not finally fight. They had quite a number of on-and-off fights over centuries. It has to be noted that there were never fights between Rome and the Etruscans as such. They involved a single Etruscan city or a limited number of them. There was not a united Etruria. It was a collection of independent city-states and there were 12 cities which were the richest and most powerful ones. They never fought altogether and there was never an all-Etruscan military force. Ancient historians at times got confused and were confusing because they reported fights with the Etruscans without specifying which city/cities were involved.

The Etruscans most probably never conquered/ruled Rome. This fashionable theory and its flimsy evidence base has been challenged recently . Unfortunately, what were mere hypotheses were often presented as actual matters of fact/historical 'truths', even though the materials used for it were nothing more than hooks for speculation, rather than actual proof. Similarly, Rome never conquered Etruria as such.

There were quite a number of wars.

The cities of Tarquinii and Veii attacked Rome when the republic was founded (509 BC) and the city of Clusium besieged it the next year.

In 396 BC, Rome destroyed the city of Veii after some 450 years of on-and-off clashes.

In 389 BC some unspecified Etruscans besieged Sutrium, a city allied to Rome. The Romans freed it and then seized two towns in the territory of Tarquinii. Soon after, unspecified Etruscans attacked two cities allied to Rome (one was Sutrium again) and were defeated.

In 358 BC Rome declared war on Tarquinii because it had raided Roman territory. This city was then joined by the city of Caere, traditionally an ally of Rome. They lost and they signed peace treaties of 40 and 100 years respectively.

In 310 BC 4 of the 5 Etruscan cities on the plateau of the Apennine Mountains besieged Sutrium. Rome defeated them and ravaged the territory of Volsinii. A few years later, the Romans came to the aid of the ruling class of this city which was facing a revolution. They suppressed it and decided to destroy the city and relocate it to a defenceless position.

The last war saw Rome defeating an army of Etruscans (probably formed by the 5 cities on the plateau) and Umbrians which was in an alliance with the Samnite and Gaul armies during the 3rd Samnite war. After that the Etruscan civilisation slowly decayed and disappeared. It had been weakened by the above wars and Rome now had hegemony in Italy. Etruria became a backwater in a peninsula that was now centred around Rome. As they were no longer troublesome, Rome did not attack them or try to conquer them.