Perhaps an interesting debate regarding the world of EVE is the exploration of the relationship between nation, state, and civilization with regards to the four main factions (and perhaps others) in New Eden. It must be noted that the idea of a "nation-state" (along with the idea of citizenship) is an inherently Western idea, and the oft-limiting but nonetheless unavoidable ethnocentrism present in the interpretation of PF thus shapes our views of the empires when it comes to this topic. It's also somewhat problematic in the sense that these are planetary concepts being applied to multi-planetary entities; it could be said the topic is useless to explore then, but for the sake of discussion, I'm going to share some ideas anyway.
Nation-state, quite obviously, infers the union of the nation and state. Britain or England would be the nation; the United Kingdom of Great Britain and Northern Ireland would be the state. The UK can be said to be complex due to the presence of multiple nations yet one nation amongst its stately borders. England, Scotland, Ireland, and Wales are the nations, and then there is Britain, which some may say is also a nation, while others will argue that it is just a state. The Hapsburg Empire is another example; Austria before 1914 was a state, not a nation. The nation is ethereal; the state is not.
Many nation-states outside of Europe are suffering from domestic troubles due to the imposing of this 'nation-state' idea onto cultures that do not share the concept. Afghanistan, for example, is neither a nation nor a state, yet it has been constructed artificially to be both. Then there is the People's Republic of China, which has rejected the Western idea of the 'nation-state' and become something more of a civilization-state; the continuation of the ancient Chinese civilization via the contemporary mechanistic construction of a state. With the idea that the 'nation-state' is thus a Western idea, how would the four major factions of EVE approach this topic?
The Amarr Empire is perhaps a good example of a civilization-state. It is the continuation of the ancient Amarr civilization from their island across multiple different systems. I would argue it is not a 'nation' because that infers the existence of other nations, for which, I reckon, were simply not considerations before first contact with the Gallente Federation. Its existence as a 'state' would perhaps only apply after the Gallente-engineered modern diplomatic system emerged with CONCORD, which specifically identifies four or five 'nation-states' as sovereign entities.
The Minmatar Republic would be a great example of imposing the idea of a nation-state onto a civilization/culture that does not subscribe to the idea (at least originally; the PF identifies many Minmatar who reject tribalism and instead support the Republic). It falls apart due to the lack of information about how the tribes are regarded domestically, and the subjective nature of their definitions. Can each of the tribes be identified as "nations", even when "nation" infers an ascension from traditional tribalism? That question is asked through the interpretation that these tribes are similar to Earth ones. I would perhaps subscribe to the idea that's already been brought up in PF (Minmatar Nation vs Minmatar Republic), that "Minmatar" itself is the nation made up of seven tribes, with the "state" the Gallente-imposed idea of the Republic (of which would not exist otherwise).
The Caldari State is interesting, too. You have a band of eight megacorporations that identify as Caldari. Perhaps the Caldari State is the nation and the eight megacorporations are the states? There is also the complex issue of states in the Federation that identify as Caldari, throwing up the true claim to the Caldari nation (the State will naturally try to claim it the rightful successor of course).
The Gallente Federation appears to be a union of nation-states, and specifically seems to identify the 'nation-state' as the only acceptable standard for a culture or civilization to abide by. This seems to be the inherent troubles the Gallente have within their borders; it's more than likely that just as Earth's idea of the 'nation-state' is Western, that New Eden's idea of the 'nation-state' is a Gallente construct. The Federation thus has the issue of trying to impose the 'nation-state' on all of its constituent parts, the idea that a nation is civilized once it has become a state. It seems to have withdrawn from this practice (at least overtly) with the ascension of the Jin-Mei, who appear as a nation or civilization.
Concluding, I don't think the idea of 'nation-state' can be applied to the Amarr, Caldari, or Minmatar, or even the Federation (except when you look at its constituent parts). The Amarr are a continuous civilization, the Minmatar a nation of seven tribes, and the Caldari an anomaly due to its megacorporate format. I brought it up nonetheless, because we use the term 'nation-states' to describe the four empires, when none of them truly are. Of course, this is just an Ivory Tower discussion; they will nonetheless be referred to as 'nation-states' due to the inherent requirement of keeping such concepts at a ground level of entry, and not make them incessantly complex for consumers of the PF. At least from the outset; I think it's definitely a point of complex discussion in-character, for example. Perhaps we can assume that the idea of CONCORD being potentially seen as an extension of Gallente political ideology is what has created the idea that the four empires are 'nation-states'; it's just that there are no attempts (at least no successful ones) by the Gallente to actually shape these other societies to abide by the Federation definition of the 'nation-state'.
Addendum: There is, of course, the idea that these are empires of star systems, each with different internal formats. The Amarr Empire being the Amarr civilization who claim Amarr space. The Caldari State being eight megacorporations of Caldari origin who claim Caldari space. The Minmatar Republic being seven tribes of Minmatar origin who claim Minmatar space. The Gallente Federation being nation-states of multiple origins who claim Gallente space. Not that I'm attempting to make what I just wrote at length to be redundant...