I’ve read the US expansion west was the second fastest permanent land expansion conquest, after Russia’s expansion through the Steppe and across Siberia.

However the Steppe historically have founded many disruptive groups that fought back and expanded into Europe and Asia.

Why was the Russian expansion so quick given the various challenges faced in Russia? Was it the result of new technologies proving imbalances between sides or a long term decline with these groups due to pressures from settled populations. When did these occur and if much earlier why did other nations not expand into the Steppe?

Thanks for any insight you can provide.