system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How/Why is Russia so big?

I do not understand.
gpt
Over centuries, the principality known as Muscovy (Moscow) expanded territorially--to the Baltic, southwest through Ukraine and Crimea, and east and south. Expansion westward and southward more or less met its end when Russians ran into Poles, Swedes, Germans, Turks, and so forth--organized states/empires who were powerful enough to counter expansion and maintain a border. To the east and southeast, there wasn't much in the way of powerful, organized states. Siberia was sparsely populated by small societies, and the nomads on the steppes in central Asia (what's now the "Stans") weren't able to effectively resist domination from a modernizing imperial power. Russian expansion halted when it met natural barriers (Pacific/Arctic Ocean, mountains) or large power further east (China, Japan). Most of this went on while other European powers (and later the US and Japan) were expanding abroad--European expansion wasn't possible for Britain or France, but their navies and access to the Atlantic/warm-weather ports (something Russia always craved) meant that expansion overseas in the Americas/Africa/Asia was possible, especially after industrialization and power projection capabilities improved.

**tld;dr**The lands east of Moscow are pretty sparsely populated, so there was little resistance to expansion.