International or Belarusian online resources dealing with the history of the Russian Empire, mostly in Russian language:

Two databases of the Russian Empire servicemen wounded during the WWI: 1914.svrt.ru and gwar.mil.ru

Russian Empire servicemen decorated with a St.George Cross numismat.ru

Soviet-Polish war 1919-1920, losses genealodzy.pl

Database of the citizens of the USSR who went through the repressions between 1920s and 1950s lists.memo.ru and throughout the 20th century visz.nlr.ru.

People from Belarus https://by.openlist.wiki and Russia https://ru.openlist.wiki who were repressed.

Database of the Soviet citizens decorated during the Great Patriotic War 1941-1945 podvignaroda.mil.ru

Drezden Database on German and Soviet POWs in 1941-1945 www.dokst.ru

Soviet army servicemen who got wounded, killed or missing in action obd-memorial.ru

General Great Patriotic War database pamyat-naroda.ru

The Russian State Military Archive rgvarchive.ru

Leningrad seige victims visz.nlr.ru

Russian search service Zhdi Menya poisk.vid.ru

Russia Genealogy Portal vgd.ru

The Belarusian nobility genealogy website nobility.by

Genealogy news in Belarus radawod.by

Soviet War in Finland (1939-1940), losses winterwar.karelia.ru and Soviet POWs who died in Finland 1941-1944 kronos.narc.fi

1943-1945 Red Army units and field postal units soldat.ru

Online cemetery index of Belarus niekropali.by and another one with GPS-tags of the graves graves.by

Vilejka area genealogy and history website vilejski-uezd.by

Online resources on geography of Belarus:

Online searcheable Polish database kami.net.pl/kresy (in English and Polish) that allows to pinpoint towns and villages.

Russian database of the Russian maps from all eras etomesto.ru. Some allow a comparison search using old and modern maps.

Two Polish databases listing maps of Poland igrek.amzp.pl and english.mapywig.org

Belarusian database of historic maps of Belarus karty.by

Belarusian database of historic areas and towns and local genealogy allowing a search radzima.net

Offline resources (archives and agencies) of Belarus (they read English but reply in Russian, message me for help):

National Historic Archive of Belarus, Minsk Branch: 55 Kropotkina Street, 220002 Minsk, Belarus (niab at niab.by)

National Historic Archive of Belarus, Grodno Branch: 21 Gospodarchaya Street, 230005 Grodno, Belarus (niab_grodno at tut.by)

There is a dozen smaller province archives but ideally you should start with the bigger places which will guide you through.

Offline resources (archives) of the nearby countries (Poland, Lithuania, Latvia, Russia):

Lithuanian State Historical Archives: Mindaugo 8, LT-03107 Vilnius, Lithuania istorijos.archyvas at lvia.lt

Poland, Central Archives of Historical Records: Długa 7 Street, PL 00-263 Warszawa, Poland

Latvia, National Historic Archives and their databases

Russian State Military Historic Archive: 3 2nd Baumanskaya Street, 107005 Russia 

Russian State History Archive: 36 Zanevsky Avenue, St.Petersburg, Russia 

Last but not least, contact your private guide in Minsk to deal with the logistics of your Belarus ancestry trip!

To sort things and ways out, to talk and be heard, join up my Facebook group Belarus family roots to learn more!