I know it is a useful shorthand, but is it really to accurate to say France and England went to war in a time where some specific man held the English Crown, French titles, and a colorable claim to the French crown declared war on the current French monarch?
This man may have had bitter enemies amongst the English nobility and strong supporters amongst the French nobility.
Or we can take an older example. Khosrau II of the Sassanid Empire sought the help of Emperor Maurice of the Byzantines to regain the Sassanid throne.
After Maurice was killed, Khosrau ostensibly fought to enthrone his son.
So would it be accurate to say that the Sassanids and Byzantines were at war? Would it be more accurate to say Khosrau warred with Phocas, and then later Heraclius?
Am I putting too much focus on the individual? Am I putting too much focus on the stated reasons for going to war?
I think your standards of what constitutes a war between two parties may be too high:just because the political entity of medieval France was not ideologically organized along the same lines add it is today doesn't mean it didn't exist, and those at the time certainly saw such wars as between England and France. Furthermore, disunity within a political entity does not preclude that entity from being considered to be in a state of war--the existence of Osmund Murrey does not mean that Britain was not at war with Nazi Germany.
I understand where you are coming from, but I feel you may be setting the bar too high.
What you're asking about is really two questions that are closely related: what constitutes a political unit, and what constitutes war?
A political unit does not have to be a nation-state. Most states today are not nation-states—many states are multinational or do not have a nation that is coterminous with their borders. For example, we might argue that the USSR never solved its nationalities problem, and was a multinational state, which ultimately shaped its unraveling. We might even tendentiously argue that Canada is a multinational state—one English speaking, the other French speaking. We can look at the PRC and Taiwan—both assert that there is one China, but they are certainly separate nations. We can look at the Kurds—a nation split across four states: Iran, Iraq, Syria, and Turkey. This is a lengthy way of saying that nation-states are historically rare, and that most states even today are not necessarily nation-states.
So, we are looking at certain types of political units. States are the modern political unit that we are familiar with, but they began to emerge really in the Early Modern period in Europe (very roughly, around 1500). But certainly there were political units before the modern state: kingdoms, empires, city-states, universalist theocratic churches, city leagues, tribes, and so on. All of these were political actors and coherent enough that we can speak of them as political units. Certainly comparable in their coherence to the modern state, eroded as it is by the transnational forces of globalization.
What makes a political unit? Here I'm going to turn to a controversial source—a German jurist, Carl Schmitt, who was a conservative before WWII, but did end up joining the Nazi Party in 1933—to try to get at "the political." For Schmitt, "the political" comes down to the ability to make a distinction between friend and enemy.
The specific political distinction to which political actions and motives can be reduced is that between friend and enemy. This provides a definition in the sense of a criterion and not as an exhaustive definition or one indicative of substantial content.
The distinction of friend and enemy denotes the utmost degree of intensity of a union or separation, of an association or dissociation. It can exist theoretically and practically, without having simultaneously to draw upon all those moral, aesthetic, economic, or other distinctions. The political enemy need no be morally evil, or aesthetically ugly; he need not appear as an economic competitor, and it may even be advantageous to engage with him in business transactions. But he is, nevertheless, the other, the stranger; and it is sufficient for his nature that he is, in a specially intense way, existentially something different and alien, so that in the extreme case conflicts with him are possible. These can neither be decided by a previously determined general norm nor by the judgement of a disinterested and therefore neutral third party.
Each participant is in a position to judge whether the adversary intends to negate his opponent's way of life and therefore must be repulsed or fought in order to preserve one's own form of existence.
An enemy exists only when, at least potentially, one fighting collectivity of people confronts a similar collectivity. The enemy is hostis, not inimicus in the broader sense; πολέμιος, not ἐχθρός.
In his Republic (Bk. V, Ch. XVI, 470) Plato strongly emphasizes the contrast between the public enemy (πολέμιος) and the private one (ἐχθρός), but in connection with the other antithesis of war (πόλεμος) and insurrection, upheaval, rebellion, civil war (στάσις). Real war for Plato is a war between Hellenes and Barbarians only (those who are “by nature enemies”), whereas conflicts among Hellenes are for him discords (στάσεις). The thought expressed here is that a people cannot wage war against itself and a civil war is only a self-laceration and it does not signify that perhaps a new state or even a new people is being created.
War is neither the aim nor the purpose nor even the very content of politics. But as an ever-present possibility it is the leading presupposition which determines in a characteristic way human action and thinking and thereby creates a specifically political behavior.
This grouping is therefore always the decisive human grouping, the political entity. If such an entity exists at all, it is always the decisive entity, and it is sovereign in the sense that the decision about critical situations, even if it is the exception, must always necessarily reside there.
These snippets are taken from Carl Schmitt's The Concept of the Political (1932). What they outline is that the political unit is brought into being by the possibility of existential conflict between collectivities and the ability for that collectivity to decide upon the public enemy. For Schmitt, sovereignty is the ability to make that decision, especially in exceptional circumstances (something he goes into more specifically in his earlier essay Political Theology (1922)). The possibility of existential conflict arises from the intense difference of the other.
Now, while Schmitt's focus was the modern state, his concept of the political allows us to examine prior groupings to see if they can be considered political units.
A kingdom or empire does seem to have a sovereign in the position to decide upon the public enemy and marshal forces to engage that enemy in war if necessary. We can see that in France of the 1400s, the Northern Italian city-states of the 1400s, the Persian empire, the Mongol Empire, the Aztec city-states, the various Chinese dynasties, the Zulu Empire, the Abbasid Caliphate, and so on.
The feudal system in Europe is more difficult, because it had overlapping and unclear lines of authority. Kings and princes, the Holy Roman Emperor, the Pope and Catholic Church, city-states, and so on. Moreover, many of the various nobles had non-contiguous holdings that had no ethno-linguistic or religious coherence. Different authorities existed that could call for war, but who the actual decision to go to war lay with could be unclear.
Nevertheless, if the people themselves were not organized into politically coherent units, the nobles still exercised something like sovereignty. Instead of saying France went to war with Spain, we might more accurately talk about conflict between the House of Bourbon and House of Habsburg, or that King Louis XIV went to war against Emperor Ferdinand III. This would be more appropriate for the transition period from feudalism to the early modern state because sovereignty was invested in the person of the sovereign rather than in the territory/people/state/nation.
Let's close then thinking about what violence would be called without coherent political units. Returning to Hellenic thought, we find that the concept of "war" depended on a prior understanding of the "polis." The polis—the basic political unit of Hellas—made the organized violence of war distinguishable from piracy, frontier skirmishes, raids, and pillaging. We can then go back to Schmitt, and see in his work that he believes the major achievement of Jus Publicum Europaeum and the sovereign state was the bracketing of violence—that war was fought between two organized armies and did not aim at reducing and exterminating its enemies and was not indiscriminate in its targets.
War and organized political units are two sides of the same coin; each is the condition of possibility for the other.
tl;dr: no, it's not wrong, although feudalism is a bit tricky
If you would like to read more about this subject, check out:
In terms of the Byzantines and the Sassanians the term that exists for this is that they are "Late Antique States." Late Antique States are characterized by religiously oriented rule, highly organized bureaucracies capable of, for instance, unified coinage and taxation, and other features that make it very much appropriate to say "the Byzantines were at war with the Sassanians."
The problem is that not all political entities of this era fit that mold. An open question, for example, to which there is no certain answer is if, when, and where the Arabs became a late antique state. In the west, for instance, the Arab armies fought pitched battles against the Byzantines at places like Yarmouk that look like inter-state conflicts. The raids into Persia, on the other hand, don't look much different from the tribal raids that had been going on for centuries, except in terms of scale and permanence. And even in the western parts of the, now Arab, empire, they essentially coopted Byzantine administration rather than introducing new forms of it. Coinage, for instance, essentially copied old Byzantine models for about a century before being Arabized and Islamized.
But again, to your question, the fact that they even bothered to Arabize and Islamize coinage (or that coinage in the Byzantine empire, likewise had explicitly religious and political propaganda elements) is indicative of state action.