(Subplot)
"May I ask what you need so many Rubles for?" Sergei asked curiously, as foreigners usually used their own country's currency.
Rubles were only used for circulation among the public; large transactions typically involved British Pounds or Spanish silver dollars, the former being on a gold standard!
Western currencies were a chaotic mess since anyone with a Gold Mountain or Silver Mountain could mint their own money.
America was the last country to adopt the gold standard, initially using foreign currencies (Spanish silver dollars), with its own currency being silver coins and local currency.
With the California Gold Rush phenomenon, the emergence of California gold coins suddenly solved America's gold shortage problem.
A civil war then returned America to its original state, and to deal with the dire situation, Lincoln greenbacks (IOUs) were introduced—if you won, they were cashed; if you lost, they were just paper.