At a press conference in October 2014, President Lukashenko (in Belarusian, Lukashenka) said "Smolensk and Bryansk are ours, but Belarus doesn't need them right now."
http://windowoneurasia2.blogspot.com.ee/2014/10/window-on-eurasia-smolensk-and-bryansk.html
These remarks led me to consider this question: What would be the maximum-sized Belarus of the 20th and 21st centuries? Political exiles from eastern Europe during the Cold War often produced maps showing how far their homelands would extend if ethnographic principles had been properly applied. Not surprisingly, those maps always showed the countries as "ideally" being much bigger than they actually were. For example, take this map, reproduced in Nicholas P. Vakar, *Belorussia: The Making of a Nation, * p. 9:
Note that this map involves major territorial claims against not only Russia (Bryansk, Smolensk, etc.) but against Poland (Bialystok, Augustowo, Suwalki), Lithuania (Vilnius/Vilno and Švenčionys/Svianciany) and Latvia (Daugavpils/Dvinsk).
What were the chances of Belarus getting all these areas? So far as the claims against Russia in the East are concerned, the only way I can see them being fully realized is if Germany wins World War I and creates a puppet Belarusian state which it wants to extend as far east as possible in order to further weaken defeated Russia.
What about the claims against Poland? Bialystok was indeed made part of the Belorussian SSR in 1939-41. Stalin might have insisted on keeping it in 1945 but "generously" conceded it to Poland as being west of the Curzon line. No real loss, he must have thought, since we will dominate Poland anyway...
Vilnius/Vilna/Wilno is an interesting possibility. Though the city itself was mostly Polish and Jewish (before the Holocaust) the 1897 census of the Russian Empire does give the Belarusians as the largest single ethnolinguistic group in the Vilna *district* (including the city): 93,896 Belarusians, 77,224 Jews, 76,143 Lithuanians, 73,088 Poles, 37,906 Russians.
http://demoscope.ru/weekly/ssp/rus_lan_97_uezd_eng.php?reg=90 (It is almost needless to say that the Polish census of 1921 gave a very different picture, and showed the district as overwhelmingly Polish. For one thing, the Poles counted Catholic Belarusians as Poles...) In 1939, when Soviet troops occupied Vilinius, the Soviets, instead of incorporating it into the Belorussian SSR, gave it to Lithuania (which they knew they would soon absorb). Molotov actually sounded a little bit apologetic to the Belarusians in explaining this decision to the Supreme Soviet: "The Vilnia territory belongs to Lithuania not by reason of population. No, we know that the majority of population in that region is not Lithuanian. But the historical past and aspirations of the Lithuanian nation have been intimately connected with the city of Vilnia, and the Government of the USSR considered it necessary to honor these moral factors."
http://thepointjournal.com/fa/library/breview-214.pdf As the Soviet press reminded Belarusians, the Soviets had conceded Vilna to Lithuania in the 1920 Soviet-Lithuanian treaty, and "the word of the Soviets is inviolable"...
(Belarusian nationalists, incidentally, have a reply to the argument that Vilna/Vilnius was Lithuania's historic capital: they maintain that the Grand Duchy of Lithuania was not a "Lithuanian" state in the modern ethnolinguistic sense, that the majority of its population was East Slavic, that before Lithuania was Polonized its official language was a form of proto-Belarusian
https://en.wikipedia.org/wiki/Ruthenian_language etc.)
Daugavpils/Dvinsk is probably the weakest of the claims, ethnographically speaking: the 1897 census showed only 32,714 Belarusian-speakers in the district, compared to 36,186 Russian speakers, 92,527 Latvian speakers, 47,486 Yiddish-speakers, and 21,662 Polish-speakers.
http://demoscope.ru/weekly/ssp/rus_lan_97_uezd_eng.php?reg=126 In the actual city of Daugavpils/Dvinsk, the number of Belarusians and Latvians was negligible; Jews were by far the largest single group, with Russians second.
http://demoscope.ru/weekly/ssp/rus_lan_97_uezd_eng.php?reg=127 The only way I can see Belarus getting the area is if the Soviets are somehow both weak enough that they have to concede Latvia's independence, yet strong enough to deprive it of Daugavpils.
To complicate matters still further: Some Belrausians even argued that Belarus should have gotten the Kaliningrad Oblast and a corridor leading to it. Vakar (p. 279) quotes emigre publications as arguing that East Prussia (or at least part of it) would be a "just compensation for the enormous devastation which Belorussia suffered at the hands of the Germans" and would give Belorussia "a sea outlet necessary for its economic development." Note also this, another émigré map of "ethnographic" Belarus:
The author of the map complains that although Russians and Belarusians jointly colonized the Kaliningrad area after the expulsion of the Germans, the ethnic character was later changed in "the interest of Russian imperialism." Note also that the map shows Belarus claiming territory not only from Russia, Poland, Lithuania, and Latvia, but even a bit from Ukraine in the Chernigov area.
Incidentally, probably the Belarusian state which on paper came closest to having the borders Belarusian nationalists wanted was the stillborn first Belorussian Soviet Socialist Republic of January 1919. Its borders were "a nationalist's dream. Based on the ethnographical maximalism of coopted intellectuals like Efim Karski (see below), the Bolsheviks' definition of their new Belarus included Minsk, Mahilew, Hrodna, Vitsebsk (though not Latgallia), a good part of Smolensk, and parts of Kaunas, Vilna and Suwalki; and even the mixed Belarusian-Ukrainian lands of Chernihiv. But the government headed by Zmitser Zhylunovich — a Belarusian writer, but based in Moscow, only lasted two weeks, and never really controlled any of its would-be territory. Smolensk was soon reassigned to Russia. The first Belarusian Soviet Socialist Republic was a will-o'-the-wisp..." Andrew Wilson, *Belarus: The Last European Dictatorship,* p. 97
https://books.google.com/books?id=jZJntMQtkSYC&pg=PA97