The easy answer to this question is no. Although the joint invasion ended the Polish government, there was a Polish government-in-exile that enjoyed broad foreign recognition for most of the war. The London Poles, as they were called, acted as the legitimate face of the Polish people and they only became sidelined in terms of diplomatic recognition when it became clear that Stalin was going to establish his own Polish government. The General Government (GG) of Germany never pretended to be a Polish state and had none of the trappings of an independent state.

But the falling diplomatic status of the London Poles and the emigres outside of Poland says little about the actual experience of the millions of Poles under foreign occupation. Here the situation is a little more convoluted.

Part of what makes this such complicated question since "nation" in English usage often has holistic connotations that muddy the waters when dealing with a question like "did Poland temporarily cease to be a nation during the war?" English usage of nation often mingles both residents of a polity and the existing state where they blend together. Terms like "nation-building" often assume building up governmental infrastructure and inculcating a sense of national cohesiveness in American political discourse. Likewise, "nation" can easily be a substitute term for "people" in the English and French lexicon. In contrast, Central and Eastern European political language instead makes a sharper division between these two. For example, German in this period used Volk and Staat to differentiate between the two, as does Russian with the distinction between narod and gosudarstvo While this division was never set in stone and constantly fluctuated, it shows a different approach to this issue of a nation than Western European and American practice.

This more bifurcated division in the terminology between the organs of government and the people it governs helps illuminate the nature of foreign rule in occupied Poland. While nation in English implies that every nation should have its own state, such sentiments were really not in operation under the occupation regimes. For example, in the German half of Poland, the overarching assumption was that while the Polish nation still existed, it no longer had a state. The German occupation regimes, whether the new Gaue or the General Government, instituted a racial classification system that defined the population according to the Third Reich's system of racial hierarchy. The SS's Volksliste sought to identify elements of the population that could be Germanized, which of course assumes that there still was a Polish nation that still existed within the German sphere of influence. Various SS and other resettlement agencies like RuSHA envisioned winnowing out the remaining "resistant" Poles to the bare minimum number needed for a helot race. So it was not a contradiction in this paradigm for the German occupation regime to use Poles at the lower rungs of the GG's civil service such as the Blue Police; Poles might participate in the occupation Staat, but the Polish Volk were clearly in a subordinate position.

The General Government itself was an anomalous position within the organizational hierarchy of the Third Reich. In more than a few ways it was an extemporized entity that incorporated a geographic space that could not be easily rationalized as belonging to Germany. The SS and other Nazi elites including Hitler spoke the GG as a racial dumping ground for undesirables and as a resource for personal and state enrichment. The GG's head, Hans Frank, though did not desire to rule over a rump state and toyed with grander ambitions. While Frank was one of the more venal Nazi officials- one nickname for the GG was "Frankreich" (a play on the word for France and Frank's empire)-the GG head envisioned it as being an entity that would spearhead a German-defined and controlled Poland in the new European order. Frank's public row with the SS in 1941/42 made him something of an opposition figure within the Third Reich, especially those that realized that racialist discrimination against Slavs meant Germany could not harness their occupied population effectively. But even Frank's most Polonophile sentiments still classified Poles as racial inferiors and his arguments for an expanded GG fell far short of being a true Polish nation in the Western meaning of the term. Nor did the GG manage to accrue much in the way of meaningful allies among the Polish population. Frank's perceived softness towards Poles as well as rivalries with the SS also led to his star being on the wane in the Third Reich's power structure, although he retained his titles and position.

The brief Soviet occupation of Eastern Poland likewise treated the annexed Polish territory as "not Poland." The official Soviet explanation for the invasion in 1939 was that since the Polish government had ceased to exist, there was no more Polish state. Like the Third Reich, the Soviets did not deign to pretend the Polish people had simply vanished. Soviet policies on ethnicity were already well-established by 1939 and the Soviet state defined nationality as contingent on a conglomeration of linguistic, geographic, and historical factors. But while these categories seem scientific and immutable, Stalinist definitions of nationalities often stacked the deck in favor of the state's priorities. Stalin was famous for redefining certain boundaries as "ancient Slavic soil," even when the historical record made these claims suspect.

The 1939 Soviet experience exemplified these tendencies. The Soviet state held that its invasion was recovering lost territory of both the Belorussian and Ukrainian SSRs which a counter-revolutionary Polish state had stolen during the Civil War. Poles in this region may have been tolerated in theory as a recognized national minority in these regions, but the immediate context and justification of the Soviet occupation rendered them an ideologically suspect nationality. Nor was the Soviet's position on non-Polish nationalist groups in the region very friendly. The Soviet approach to nationality held that nationalism was acceptable when under the auspices of the Communist Party. The Soviet policy of Korenizatsiia'- termed by Terry Martin as Soviet affirmative action- allowed for national development, but only when mediated by the Party since nationalism could easily give way to chauvinism and other counter-revolutionary thought.

These Soviet and German practices of classifying whole ethnic groups as either class or racial enemies was part of the reason why the occupation of Poland became so violent. Creating a hierarchy of favored and unfavored subject peoples encouraged a dissolution of social relations on the ground. Food requisitions, collectivization, and a whole panoply of discriminatory practices provided an incentive for communities to turn on each other to gain a brief advantage. Locking these peoples into a subservient position in the state order also fostered a destructive social anomie and an us-vs-them mentality. The foreign occupiers may have been the enemy, but so too were their perceived allies among other non-Polish ethnic groups.

Sources

Gross, Jan Tomasz. Revolution from Abroad: The Soviet Conquest of Poland's Western Ukraine and Western Belorussia. Princeton: Princeton University Press, 2002.

Mazower, Mark. Hitler's Empire: Nazi Rule in Occupied Europe. New York: Penguin Books, 2009.

Winstone, Martin. The Dark Heart of Hitler's Europe: Nazi Rule in Poland Under the General Government. London: IB Taurus, 2015.