The Lithuanian lands were consolidated in the 12th Century and by the 15th Century it had expanded to become the largest state in Europe. In the Union of Lublin, the Grand Duchy of Lithuania joined the Kingdom of Poland forming the Dual Commonwealth. Despite the union, territories and institutions in the Dual Commonwealth were kept separated as either part of the Grand Duchy of Lithuania or the Kingdom of Poland. Inside the Dual Commonwealth, some of the Grand Duchy lands, mainly those in the South where incorporated as part of the Kingdom of Poland under the generic name of Rhutenia.
In late 18th century Russia was partitioned between the Dual Commonwealth, Sweden and Sibiria. The Dual Commonwealth annexed south and central Russia, including Muscovy. Except for some southern parts, most of the annexed Russian territory, including Muscovy, where incorporated to the Grand Duchy. However by this time the distinction between the Grand Duchy and the Kingdom were mostly traditional.
During the Great War of 1912, the Commonwealth was severely beaten by the Allied Powers, Lithuanian nationalism was a decisive factor to break the union, but Ruthenian and Russian nationalism were also important. This situation lead the Commonwealth to surrender in 1916, a couple of months earlier than co-belligerents Austria and France.
The Commonwealth had no functional government, but neither had the regions. During the Frankfurt conferences different alternatives were proposed on how to partition the Commonwealth. The Final proposal included to first follow the division between the Crown and Lithuania, and then, inside Lithuania, to secede pre-1768 Russia from Lithuania proper, and inside the crown to separate the west-Slavic territories (Poland) from the east-Slavic ones (Ruthenia).
The pact was signed in December 1917, but soon several wars sparkled between the different new states.
Several Lithuanian provinces, usually known as White Ruthenia, had demanded either to be part of the Ruthenian state or to form their own state. After the Ruthenian defeat against Russia, White Ruthenian provinces demanded rather autonomy than annexation to the southern fellow country.
The tension grew, and the Lithuanian government massacred over 1000 non-combatant White Ruthenians in 1919. This triggered a war between Ruthenia and Lithuania, passively followed by the neighboring countries.
After three years of fighting, an almost defeated Lithuania finally broke the Ruthenian front. There was not a decisive military victory but Ruthenia finances were on the edge and the perspective of a longer war forced a collapse in the economy. Negotiations began, and the peace of Warsaw was signed between the fighting powers.
Lithuania transferred several White Ruthenian provinces to the Ruthenian Republic, but kept those closer to Vilnius.
In 1943, Lithuania signed a military alliance with the Swedish Commonwealth, and is a founder member of the Baltic Common Market.