International or Belarusian online resources dealing with the history of the Russian Empire, mostly in Russian language:
Russian Empire servicemen decorated with a St.George Cross numismat.ru
Soviet-Polish war 1919-1920, losses genealodzy.pl
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
1943-1945 Red Army units and field postal units soldat.ru
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.
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
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!