The Romans and Greeks talk about the "Gauls" as if they are one people, living in a territory as widespread as France and the low countries, to northern Italy, and down into the Balkans. There were also the "Celtiberians"; living in modern Spain, and the "Galatians"; who had settled in central Anatolia. Were these far flung tribes ever united as part of a greater Gaelic confederation or empire?
During the wars with Rome, Vercingetorix was declared king, and united the tribes of Gaul and fielded several armies against the Romans. Was this kingship a tradition the Gauls had practiced before? With the political division of Caesar's time being abnormal? Or was this unity simy brought on by the necessity of the Roman invasion?
More can be said or asked about it, but you might be interested on these previous posts.
In short (but you'd get much more details from these linked posts) while division and infighting amongst Gaulish petty-states was a staple of Gaul's political life, it wasn't necessarily contradictory to a sense of broader cultural, religious, economical or political commonality, as it can also be observed in ancient Greece or ancient Etruria : regional hegemonies (such as the Aedun hegemony in central Gaul), confederations, alliances, common monetary area, etc. and when it comes to broader regions, Druidic (for religious, diplomatic and judicial purposes) or political assemblies (namely Pan-Gaulish, Belgian, Aremorican, possibly Celtic in the sense of central Gaul) that were tasked with both appointing a political leadership as well as organizing a military response to a percieved common threat.
It can also be observed in Galatia (as described by Strabo in Geographica; XII, 5, 1) with the Koinon Galaton, the Galatian league or commonwealth, and particularly reminiscent of the macro-regional organisation in Gaul : made of three peoples(Tectosages, Tolistoboges and Trocmoi) it had a common assembly that also dealt with high justice (similarly to both Gaulish regional assemblies and the druidic assembly) while each people had its own proper organisation and sub-divided into districts (there again, similar to Caesar's civitates and pagi). It doesn't seem, arguably, that such regional or macro-regional ensembles existed as such in Cisalpine Gaul, which is sometimes mentioned as factoring in its early conquest.
During the wars with Rome, Vercingetorix was declared king, and united the tribes of Gaul and fielded several armies against the Romans. Was this kingship a tradition the Gauls had practiced before?
A word of caution there : Vercingetorix's royal title (De Bello Gallico, VII-4) isn't directly related to his mandate as commander of the coalition he recieves shortly later on. Rather, he's proclaimed king of the Arverns (descending himself from royal lineage) as he topples the republican regime that in so far supported Romans during the Gallic Wars, although resurrecting the royal title, seemingly disappeared in 121 BCE as Arverns were defeated by Romans, certainly gave Vercingetorix enough prestige and most of all, a strong power base to be considered for receiving the leadership of the coalition.
A similar political-military personal set of leaderships can be pointed at, among other exemples, with Diviciacos as both king of the Suessiones and "most important person in Gaul".
