Why have President Obama and Russian President Dmitry Medvedev agreed to reduce their arsenals of nuclear power?

Answer 1

The mutual reduction of nuclear arms between what was then the Soviet Union and the US started in the 1950's. There were and are quite a few reasons, but probably the top reasons had to do with economics.

In the 1950's and 1960's, we already had the technology for high yield nuclear fission/fusion pretty well nailed. What we lacked was precision delivery systems. Ballistic missile attacks launch a weapon tremendously high above the earth, engines cut off, and the missile comes back to earth at near-orbital speeds -- around 30,000MPH. At that speed, even something as simple as passing though a rain storm can toss the weapon off course and at the time we didn't have anything by way of in-flight telemetry and control (the idea being that if you could control your own weapons, what if your opponent jammed or hacked you?).

he solution chosen by both sides, but moreso the USSR was to develop huge-yield warheads. That way, if you missed by a few miles it'd still effectively strike the target. The US was admitting to lofting 5 Megaton warheads; the USSR was reported to have cobalt jacketed weapons that yielded up to 360 megatons. That much fissile material is dangerous to have around and hugely expensive.

In addition to the two-way increase in warhead yield, the USSR invested heavily in solid fuel propellants. This was inexpensive at first, and didn't require the fast-fueling technology liquid fuel wanted for. But it also didn't lend itself to underground placements, and so much of the Soviet arsenal was undisguised and unhardened; easily subject to a pre-emptive first strike that would leave them unarmed and unable to respond. The solution? Build more missiles!

The effects of this direction are, in retrospect, obvious. Both sides created way more than enough weaponry to obliterate each other many times over, mostly in order to provide redundancy. This is when the phrase "overkill" was invented.

If this weren't bad enough, existing nuclear weapons, especially the solid fueled kind, need a huge amount of ongoing maintenance in order to remain flight worthy. So what had developed was a huge cash sink in the name of defense, that both primary participants agreed was something of a dead end in terms of growing the system.

Through the 1960's, targeting capabilities increased as well. And this meant that a smaller warhead, placed more accurately, could be far more effective than a huge warhead. Reduction in both the number of weapons and the size of the warheads made a lot of sense.

In 1969, the Strategic Arms Limitation Talks (SALT-I) commenced in Helsinki, Finnland, and continued on to 1972. This treaty limtied the number of Inter Continental Ballistic Missiles (ICBM's). Submarine Launched Ballistic Missiles (SLBM's) and Anti-Ballistic Missiles (ABM's). Under Jimmy Carter and Leonid Brezhnev, the SALT-II talks were signed (but not ratified) in 1979. Since then, there's been an ongoing progressions of talks limiting size, number, targeting, testing and payload between the USA and Russia, and also between the original 5 nuclear capable nations (USA, USSR/Russia, England, France and China.

While there are quite a few countries nowadays that are players on the nuclear court, only the USA and Russia appear to maintain the munitions required to stage a strategic nuclear war. And the US and Russia are no longer considered adversaries.

As such, it makes good political and economic sense to commence dismantling these giant, obsolete armories. Saves money, is cleaner, reduces the chance of a catastrophic accident... altogether probably a good thing :}