Short answers, pulled from the story.
The Great Stand on the Ugra River in 1480 marked the formal end to centuries of Tatar rule over Russia. Ivan III and Vasili III consolidated a centralized state following this event.
Peter the Great gained Livonia, Estonia, Ingria, and Karelia from Sweden following the Great Northern War and the Treaty of Nystad in 1721. This expansion secured Russian access to the Baltic Sea.
By the end of World War II, the Soviet Union had annexed territories including the Kresy from Poland, Estonia, Latvia, and Lithuania occupied in August 1940, and Bessarabia from Romania after an ultimatum in 1940. These acquisitions expanded Soviet borders significantly.
The Chechen Republic of Ichkeria existed as a secessionist government between 1991 and 2000, ending with Russia recognizing the new government in January 1997 before invading again in 1999. The conflict concluded with the reintegration of the region into the Russian Federation.
On the 21st of February 2022, Vladimir Putin signed a decree recognizing the independence of two Donbas republics in Ukraine and invaded the region. Two days later, Russian troops openly invaded Ukrainian-held territory, aiming to seize eastern and southern Ukraine right through to Transnistria.