Going back to central Russia: Moscow screw is the easy part, it only became too powerful for other Orthodox Russian principalities to overcome by the 1480s and too powerful for Poland-Lithuania alternate unifier to conquer by 1610s.
1. Moscow was far away enough from the steppe that it could avoid regular nomad pillaging that weakened Kiev, close enough to the steppe that it could be a logical point for the Golden Horde to collect tribute from Rus principalities via their vassal (unlike Novgorod) Any of the cities in the modern Central Federal District (Yaroslavl, Kostroma, Pereslavl, Tver, Vladimir, Ryazan) could have taken the same path.
2. Properly timing when to break from Mongol rule
Tver was slightly further from the steppe and Golden Horde retribution than Moscow, and at first had stronger fortifications. False confidence from this meant it was the first principality to go for independence (1327) nearly withstood the siege, but ultimately was sacked (with Moscow help) and screwed long term when the Horde gave Vladimir prince status to Moscow.
When Moscow went for independence in 1380, it also got sacked (with Ryazan help) but had a network of allies in place and a Horde distracted by Tamerlane so it recovered and sacked Ryazan.
A POD leading to more militant early 1300s Moscow rulers instead of the historical helpful vassal role Yury played —> Moscow rises first and is suppressed—>Tver unites Russia. Or Tamerlane dies early—> Horde focuses on Rus —>Ryazan helps Mongols do to Moscow what Moscow did to Tver—> with luck, Ryazan unites Russia.