Seventy years ago, the United States dropped two atomic bombs on Japan. Up to now, the US remains the only country to have used a nuclear weapon against another country.

In April 2009, US President Barack Obama called nuclear weapons "the most dangerous legacy of the Cold War." He pledged that his administration will take "concrete steps" towards "a world without a nuclear weapon"—a commitment that eventually earned him the Nobel Peace Prize.

However, at present, the US seems to be poised towards maintaining its nuclear arsenal. In fact, the Obama administration is proposing that the US government spend $1 trillion in the next three decades to buy replacement systems and even upgrade its existing nuclear bombs and warheads.

According to a study published last year by the James Martin Center for Nonproliferation Studies, the US currently "maintains a robust nuclear arsenal deployed on a triad of strategic delivery systems."

This nuclear arsenal includes land- and submarine-based long-range ballistic missiles and nuclear-capable bombers, the study stated.

The document also showed that the US government plans to procure replacement platforms and associated warheads sometime after 2020.

The National Nuclear Security Administration (NNSA), a semi-independent agency under the Department of Energy, will undertake the task of replacing existing nuclear weapons with new warheads. This will cost the US government approximately $60 billion.

The NNSA also proposed the construction of new nuclear material production facilities and the consolidation of the current stockpile of seven types of warheads into five.

The agency also envisions the US government's nuclear arsenal to be composed of three different warheads deployed on Air Force and Navy long-range missiles and two types of air-delivered weapons deployed on cruise missiles and bombers.

Aside from this, the US military budget continues to be the biggest in the world at $610 billion. This is larger than the combined military budgets of seven big countries: China, Russia, Saudi Arabia, India, France, Germany and the United Kingdom.