Belarus–Ukraine relations (, ) are foreign relations between Belarus and Ukraine. Both countries are full members of the Baku Initiative and Central European Initiative. In the waning days of 2021, the relationship between Ukraine and Russia began rapidly deteriorating, culminating in a full-scale invasion in late February 2022. Belarus has allowed the stationing of Russian troops and equipment in its territory and its use as a springboard for offensives into northern Ukraine but has denied the presence of Belarusian troops in Ukraine. Historical relations Pre-1991 background Both countries, each historically part of Kievan Rus' (9th to 13th centuries CE), came gradually under the control of the Polish–Lithuanian Commonwealth (1569-1795), and ultimately, of the Russian Empire (1721-1917). The Second Polish Republic ruled parts of each in the period from 1918 to 1939. Prior to the 1991 breakup, both countries formed part of the Soviet Union (founded in 1922) as the Byelorussian SSR (founded in 1920) and Ukrainian SSR (founded in 1919); they both became founding members of the United Nations in their own right in 1945. As Slavic nations, both Belarus and Ukraine share closely related cultures and are predominantly inhabited by the East Slavic ethnic groups of Belarusians and Ukrainians respectively. There was an extensive period of diplomatic cooperation from 1918 to 1921 when the Belarusian Democratic Republic made contacts with the Ukrainian People's Republic (UNR) and the Ukrainian State of Pavlo Skoropadsky. Skoropadsky's government made the largest overtures to the Belarusians, with him himself informally recognizing the Belarusian DR as de facto independent in October–November 1918, although de jure recognition did not materialize. The UNR, although hesitant in the beginning, ultimately attempted to follow this route in international relations after Skoropadsky's fall. During this period, although without formal recognition, both countries established diplomatic ties in May 1918, exchanged diplomatic missions, the Ukrainians provided financial assistance to the Belarusian government and there were ideas of a federated defensive alliance between Ukraine and Belarus. Modern era Today, the two countries share an 891–km border. An agreement on the state border between Belarus and Ukraine signed in 1997 was to be submitted to the Belarusian parliament for ratification after Belarusian President Alexander Lukashenko and former Ukrainian President Viktor Yushchenko finished the process of the formalization of the border issues between the two states in early November 2009. Breakdowns in relations In August 2020, during the Belarusian protests against Lukashenko, Ukraine recalled its