Due in part to its geology and its geography, North Korea was destined to be a center for nuclear development and debate.

Even before the modern state emerged, its role as a center for nuclear research was well established. Throughout World War II, Japanese officials reportedly based their efforts to develop an atomic weapon in the region due to its large natural reserves of some 26 million tons of uranium.

After the Soviets and Americans divided the Korean peninsula along the 38th parallel -- a move that was supposed to be temporary but eventually led to the development of the two Korean states -- the Soviet Union began exporting uranium out of the area. Shipments reportedly topped 9,000 tons between 1947 and 1950.

North Korea's desire for its own weapon, though, stemmed from its own military ambitions. In 1950, the North Korean army poured across the 38th parallel, invading the South and sparking a war with America. At several points during the ensuing three-year war, the U.S. military considered using atomic weapons. According to historian Bruce Cumings, Gen. Douglas MacArthur told the Department of Defense that he saw "a unique use of the atomic bomb" to strike a "blocking blow" should China enter the war.

President Truman also said in November 1950, "There has always been active consideration of [the atomic bomb's] use."

In the midst of the war, Kim Il Sung's government formed the Atomic Energy Research Institute to develop use of radioactivity in industry, medicine and agriculture. After the war ended in a bloody stalemate, North Korea continued its nuclear efforts, beginning to train nuclear engineers and scientists in the Soviet Union. Their work focused on the development of the United Institute for Nuclear Research in the Russian city of Dubna. The center served as the international nuclear research laboratory for all communist nations.

During the 1960s and '70s, Russian scientists instructed the North Koreans on plutonium-processing methods. The work culminated in the construction of the Yongbyon Nuclear Research Complex, 60 miles north of the capital Pyongyang, in 1961-62. By 1963 the first Soviet-supplied research reactor was under construction at the site.

Research continued for nearly two decades before their efforts came to fruition. According to the Congressional Research Service, the first major atomic reactor at Yongbyon was built between 1980 and 1987. This 50 megawatt reactor is reportedly capable of producing enough plutonium each year to build a single atomic weapon.

The site at Yongbyon remains at the heart of North Korea's nuclear effort, also housing two significantly larger reactors onsite that have been under construction since 1984, according to former U.S. Ambassador Robert Gallucci. If completed, these sites could produce enough fissile material for some 30 atomic bombs per year.

The site also houses a large plutonium processing plant. The 600-foot-long multi-story building reportedly houses the refining machinery to make reactor uranium rods and generate weapons-grade plutonium.

A CRS report on the site disputed North Korea's claims that Yongbyon's main goal is electricity generation.

"Satellite photographs," Larry Niksch wrote in a Jan. 7, 2003 paper, "reportedly also show that the atomic reactors have no attached power lines, which they would have if used for electrical power generation."

In 1989, the North Korean government shut down the active reactor for some 70 days. According to South Korean, Russian and American intelligence estimates, workers at Yongbyon removed the nuclear core and processed enough plutonium to construct one or two atomic bombs. By 1990, the KGB reported to the Soviet Central Committee that "development of the first nuclear device has been completed at the DPRK [Democratic People's Republic of Korea -- North Korea] nuclear research center in Yongbyon." The report went on to say the North Korean government would not test the device in order to avoid international detection.

Within a year, the Bush administration made several diplomatic overtures in the hopes of bringing North Korea into line with the nuclear Non-Proliferation Treaty, which Kim IL Sung's government had agreed to in 1985.

First, the United States removed its nuclear weapons from South Korea in late 1991. It then urged North Korea to agree to two pacts, one a denuclearization agreement with the South, the other a so-called "safeguards agreement" with the International Atomic Energy Agency. The deal with the IAEA, which required North Korea to report all nuclear programs and make those facilities open to international monitoring, led to a series of six inspections between June 1992 and February 1993.

Within months of starting the inspections, IAEA officials found evidence indicating North Korea had not fully accounted for its nuclear stockpiles. This prompted the United Nations nuclear watchdog to invoke a special inspection protocol to survey two concealed nuclear waste sites at the Yongbyon complex. North Korea rejected the IAEA request in March 1993 and promptly announced its intention to pull out of the NPT.

In 2002, President Clinton acknowledged that in the midst of this 1993-94 standoff, the president considered a plan to bomb the Yongbyon complex. Whatever plans were considered, President Clinton instead responded with a diplomatic offer of high-level negotiations, a move that caused North Korea to suspend its planned departure from the proliferation treaty.

After extended negotiation, North Korea and the United States entered into the Agreed Framework on Oct. 21, 1994. Under the deal, North Korea would suspend all work at the Yongbyon complex, end all efforts to enrich plutonium for weapons and open its facilities to international oversight. In exchange for these moves, the United States would supply North Korea with two light water reactors (LWRs) to generate electricity, and low-cost oil to help with energy needs until the reactors were built. The agreement also promised a lifting of most economic sanctions against North Korea, and improved diplomatic relations with the United States.

The main goal in offering North Korea LWRs was to eliminate the output of plutonium that could be used for weapons.

"If the two light water reactors slated to be built in North Korea are operated to optimize power production, they will discharge about 500 kg of reactor-grade plutonium a year in highly radioactive spent fuel. However, this plutonium cannot be used in nuclear weapons until it is separated from this radioactive fuel," David Albright and Holly Higgins of the Institute for Science and International Security explained in a 1997 report. "North Korea's existing reprocessing plant ... would require extensive and difficult modification to separate all this plutonium."

Although the sanctions against North Korea were largely lifted and oil deliveries began in early 1995, the development of the LWRs bogged down. The United States, South Korea, Japan and several other countries came together to form the Korean Peninsula Energy Development Organization (KEDO) to build the reactors. Bureaucratic wrangling over contracts and the establishment of KEDO slowed the process even more so that the foundations for the two reactors were not poured until August 2002.

North Korea also slowed the process by making new demands on KEDO, including that the consortium cover the costs of modernizing its electricity grid. KEDO rejected the request and North Korea countered with a demand that the United States cover the costs associated with the delayed reactors, which the United States has refused to do.

Even as the nations were debating implementation of the Agreed Framework, North Korea, the United States argued, was breaking the spirit, if not the letter, of the pact. Within months of signing the framework, North Korea and Pakistan reportedly cut a deal to trade missile technology for Pakistan's uranium enrichment techniques.

For more than three years, the North Koreans worked quietly on their uranium project while urging the United States to fully implement the Agreed Framework. According to a Chinese government report that was leaked to a Japanese newspaper, the project included a secret uranium processing facility located inside Mount Chonma, near the Chinese border.

The Clinton administration apparently learned of the secret program in late 1998 or early 1999, and by March 2000, President Clinton informed Congress he could no longer certify that "North Korea is not seeking to develop or acquire the capability to enrich uranium."

Over the next two years, the United States continued to compile evidence on North Korea's uranium project. It was this evidence that prompted President Bush to label the Kim Jong IL government part of the "axis of evil" in his 2002 State of the Union address. "Some of these regimes have been pretty quiet since September 11th. But we know their true nature. North Korea is a regime arming with missiles and weapons of mass destruction, while starving its citizens," the president said.

"States like these, and their terrorist allies, constitute an axis of evil, arming to threaten the peace of the world. By seeking weapons of mass destruction, these regimes pose a grave and growing danger," Mr. Bush added. "They could provide these arms to terrorists, giving them the means to match their hatred. They could attack our allies or attempt to blackmail the United States. In any of these cases, the price of indifference would be catastrophic."

In October 2002, Assistant Secretary of State James Kelly confronted officials in Pyongyang with U.S. evidence of the uranium project. North Korea admitted it was pursuing the program, and in December 2002 the Central Intelligence Agency reported North Korea could develop an atomic weapon by 2004.

North Korea said it would continue the program unless the United States agreed to enter into bilateral talks to draft a non-aggression pact. The United States rejected those calls since it would not include South Korea and could compromise the South's future security.

In December 2002, KEDO moved to cut off the supply of fuel oil to North Korea, citing the North's violation of the Agreed Framework. North Korea's response was swift and reportedly unexpected -- it would re-start the nuclear reactor in Yongbyon, resume construction of two larger reactors and restart the plutonium reprocessing plant that operated until 1994.

"By their own admission, Bush administration officials were surprised by the intensity of North Korea's moves in late December 2002 to restart nuclear facilities at Yongbyon and expel officials of the International Atomic Energy Agency placed there under the U.S.-North Korean Agreed Framework of 1994 to monitor the shutdown," Larry Niksch of CRS wrote in a report for Congress.

In an effort to defuse the situation, the United States, China, Russia, South Korea and Japan held repeated six-party talks aimed at ending North Korea's nuclear program, with little progress.

Then, in October 2006, North Korea claimed to have conducted its first underground nuclear test, drawing international condemnation and Washington's continued rejection of direct talks.

Days later, the U.N. Security Council voted unanimously to impose sanctions on the North, though they were designed to allow continued humanitarian aid. North Korea soon agreed to return to the six-party talks, which led to a deal in October 2007 in which the North would dismantle its Yongbyon nuclear facility and allow international inspectors into the country, in exchange for aid, trade and improved diplomatic relations.

In June 2008, North Korea handed over a long-awaited accounting of its nuclear work, fulfilling a key step in the denuclearization process. In response, President Bush said he would lift key trade sanctions against North Korea and remove it from the U.S. terrorism blacklist -- as long as the country continued to fulfill its nuclear promises.

-- Compiled by Lee Banville for the Online NewsHour