Historiographical concept
The gathering of the Russian lands or Rus' lands () was the process in which new states – usually the Principality of Moscow and the Grand Duchy of Lithuania – acquired former territories of Kievan Rus' from the 14th century onwards, claiming to be its legitimate successor. In Russian historiography, this phenomenon represented the consolidation of a national state centered on Moscow. The sobriquet gatherer of the Russian lands or Rus' Land () is also given to the grand princes of Moscow by Russian historians, especially to Ivan III. The term is also used to describe the expansion of the Grand Duchy of Lithuania into Rus' principalities; the Lithuanian grand dukes claimed authority over all territories inhabited by Rus' people (East Slavs). Some historians argue that Lithuania began "gathering Rus' lands" before Muscovy did. The rules of Moscow adopted the title "Sovereign of all Russia" (later changed to "Tsar of all Russia" and finally "Emperor and Autocrat of all Russia") while the Lithuanian Grand Dukes adopted the title "King of the Lithuanians and [many] Ruthenians" and later under the Polish–Lithuanian union as "King of Poland, Grand Prince of Lithuania, Rus', Prussia, Samogitia, Mazovia and other.
Origin of the phrase.
According to scholar Charles J. Halperin (1973, 2022), the first time the idea of gathering Rus' lands appears in writing is in the "vita" of Dmitry "Donskoy" Ivanovich, wherein his grandfather Ivan "Kalita" Danilovich is called the "gatherer of the Rus' Land". The "vita"'s dating is complicated, with Polish–Ukrainian historian Jaroslaw Pelenski (1977) concluding it was probably written in 1454 or 1455. Pelenski translated the opening passage of Donskoy's "vita" as follows: 
In historiography.
In historiography on the Principality of Moscow.
The concept arose in Russian tsarist-era historiography of the 19th century, and the term could be found in works of several historians such as Dmitry Ilovaysky, Kazimierz Waliszewski, and many others. The concept has been used to justify the liquidation of feudal fragmentation in the post-Golden Horde period.
Several historians of Muscovy/Russia have written that the process of "gathering" culminated during the reign of Ivan III (r. 1462 – 1505), in which he established a unified monarchy. Although various semi-independent princes still claimed certain territories during his reign, Ivan's overlordship was acknowledged by the princes. By the 16th century, Ivan IV (r. 1533 – 1584) became the undisputed autocratic ruler of Russia and the policy of "gathering" Russian lands helped pave the way for Russian eastward expansion, including non-Russian territories.
According to Marc Raeff, this process became indistinguishable from imperial expansion with the annexation of the Astrakhan and Kazan khanates as well as the movements of the peasants into new territories. Raeff says that "Indigenous groups mingled with Russians that had moved in, and transfers of population resulted in linguistic and cultural mixtures within the same administrative unit". As a result, "Russian society remained largely unaware of the state’s having become a multinational empire".
In historiography on the Grand Duchy of Lithuania.
In Soviet historiography in the 1980s, there were disputes between scholars over which polities had a "right" to gather the lands of Rus'. The pre-1917 tradition, as represented by Igor Grekhov, argued that the Grand Duchy of Lithuania was predominantly populated by Eastern Slavs, and was therefore a legitimate gatherer. On the other hand, the Soviet-era doctrine, as expressed by Vladimir Pashuto, regarded Moscow as the only legitimate gatherer, while Lithuania's expansion was considered to be outright aggression. Pelenski (1982, 1998) reasoned that "the claim of the Lithuanian grand princes to "all of Rus'" and their program of "gathering of all the Rus' lands," advanced even before Muscovite Rus' had developed an equivalent program of her own, promoted the Lithuanian grand principality into the role of successor state to Kievan Rus', and this represented a direct challenge to the Golden Horde."
Ukrainian historian Serhii Plokhy (2006) cited the 1338 Lithuanian–Livonian Treaty as evidence that grand duke Gediminas of Lithuania was in effect a "gatherer of the Rus' lands", as the Middle Low German text distinguished "Lettowen" ("Lithuania") and "Rusce" ("Rus'"), "Ruslande" or "Ruscelande" ("Rus' Land" or "Ruthenia") as the two parts of the realm, inhabited by "Lettowen" ("Lithuanians") and "Ruscen" ("Rus'" or "Ruthenians"), both under the "ret" ("authority") of the "koningh van Lettowen" ("king of Lithuania"), where any visiting "Dudesche kopman" ("German merchant") and their goods would be under his legal protection. Halperin (2022) questioned whether the 1338 Treaty described political rather than purely geographical dimensions of the Rus' Land. On the other hand, he confirmed that in many sources such as the Hypatian Codex (including the "Kievan Chronicle" and "Galician–Volhynian Chronicle"), the Belarusian–Lithuanian Chronicles (including the "Bychowiec Chronicle"), the "Eulogy for Vytautas", and the "Hustyn Chronicle", the term "Rus' Land" is variously used as either comprising all the Ruthenian territories of the Grand Duchy of Lithuania, or only its Belarusian territories, or (more rarely) only its Ukrainian territories, instead of Suzdalia and later Muscovy.
References.
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