Question

При каком князе границы Московского княжества наиболее расширились?

Answer 1

При Иване Калите. Т.к он присоединил к Московскому княжеству половину Ростовского княжества тем самым увеличил ее площадь чуть-ли не в двое.

Answer 2

As of my last update in September 2021, the boundaries of the Moscow Principality (Knyazhestvo) significantly expanded under the rule of Ivan III, also known as Ivan the Great (1440-1505). During his reign, Ivan III managed to annex various neighboring territories, including Novgorod, Tver, and other principalities, effectively expanding the territory of the Moscow Principality and transforming it into the Grand Duchy of Moscow.

Ivan III's marriage to Princess Sophia Palaiologina, the niece of the last Byzantine Emperor, also strengthened the cultural ties between Moscow and the Byzantine Empire. This relationship contributed to the perception of Moscow as the "Third Rome," further legitimizing its role as a prominent and influential state in the region.

It's worth noting that historical events may have occurred after my last update, so I recommend checking more recent sources for any developments beyond September 2021.