The former Soviet Union began work on its nuclear weapons program in the 1940s after hearing reports of the US Manhattan Project.
After the Soviet-US arms race during the Cold War, nuclear weapons previously stored in former Soviet states were returned to Russia where many were dismantled. But Russia still maintained a vast stockpile of weapons.
Today, Russia appears to be investing in nuclear weapons modernization — much like the US — and growing its arsenal. Last year, Obama criticized such efforts as impediments to global nuclear disarmament.
"Because of the vision that he's been pursuing of emphasizing military might," Obama said, referring to Russian President Vladimir Putin, "we have not seen the type of progress that I would have hoped for with Russia."
In October, Putin said he wants to help reduce the world's nuclear arsenal and "will be striving to achieve that," but added that Russia will continue to develop its program so long as other countries continue doing so.
While Russia has the most nuclear weapons of any country in the world, that doesn't necessarily mean they are the most powerful.
"Russia built nuclear weapons that are incremental improvements," or weapons that would need updating every decade or so, Jeffrey Lewis, the founding publisher of Arms Control Wonk, told Business Insider.
On the other hand, Lewis said, "US nukes are like Ferraris: beautiful, intricate, and designed for high performance. Experts have said the plutonium pits will last for 100s of years." Indeed, the US's stocks of Minuteman III ICBMS, despite their age, are "exquisite machinery, incredible things."
"Russia's nuclear weapons are newer, true, but they reflect the design philosophy that says 'No reason to make it super fancy because we'll just rebuild it in 10 years,'" Lewis added.