The mid-twentieth century saw an arms race on an unprecedented scale between the members of NATO and the members of the Warsaw Pact. Beyond the development of chemical, biological, and nuclear weapons, a crucial element often overlooked by historians (though rarely by strategists) in the Cold War arms race was the development of delivery systems for the world's deadliest weapons: ballistic missiles.

The concept behind ballistic missiles is simple: long-range missiles are launched into space, and guided reentry vehicles carrying chemical, biological, or nuclear weapons slip back into the earth's atmosphere and target a site of strategic interest. At the height of the Cold War, NATO and the Warsaw Pact nations remained poised and ready to launch land- and submarine-based ballistic missiles with nuclear warheads at one another. Developments in ballistic missile technology led not only to developments in propulsion, guidance systems, satellite navigation, submarines, and space exploitation, but also in theoretical methods of defense against the missiles themselves.

Following the collapse of the Soviet Empire and the Warsaw Pact, and the resulting decline in international stability, the United States initiated a renewed drive to research and implement a ballistic missile defense system. Initial setbacks eventually led to successful tests of both shore- and sea-based systems. These systems have since been integrated, featuring radar and interceptor missile systems in Alaska and California. As the U.S. Government prepares to expand the system, international debate has increased regarding the repercussions of implementing such a system.

In addition to the domestic sites, there are two major sites of implementation planned. The first site is Japan, which can be divided in twain: the Sea of Japan, and Japan proper.

The United States Navy is employing the Standard Missile family; the SM2 (Navy Fact File, Global Security) is already being employed, while the SM3 is being developed specifically for the BMD mission. These and other munitions are being coupled to the Navy's AEGIS command and control system. Several ships have already been outfitted with the program-specific equipment and deployed to the Sea of Japan. Although the system is still under development, American personnel are prepared to activate an intercept should North Korea attempt to launch an offensive strike.

Meanwhile, on the Japanese islands, Japanese and American military forces are deploying the Patriot Advanced Capability 3 system. Following North Korea's 2006 missile tests, Japanese and American officials announced the planned deployment of the PAC-3 system. The initial deployment of the Patriot system was nearing completion as of October, and in November plans were made to accelerate the implementation of the full system. One element of this acceleration was the March deployment of the PAC-3 system around Tokyo (AP, BBC), a full year ahead of schedule.

Another possible venue for a ballistic missile defense system is South Korea. However, South Korea is well within the range even of North Korea's lowest-range Hwasong 5 SCUD variants. As such, in the unlikely event that North Korea actually targeted South Korea in the first place, they would have no need to use their long-range Taepodong series missiles, which would overshoot South Korea entirely. Thus, a conventional missile defense system for South Korea would be more feasible and cost effective. Reports indicate that South Korea is seeking an independent missile defense system that would fit their unique needs.

The second and more controversial site for the overall program is in Central Europe. The plan for this system calls for a powerful new early warning radar system in the Czech Republic and a battery of interceptor missiles in Poland. There has also been discussion of basing part of the system in the United Kingdom (BBC, Financial Times), which is the site of the newly upgraded early-warning radar facility at Fylingdales in Yorkshire.

The BBC has a simple but informative animated presentation on how the system will work; for the more dedicated researcher, Global Security features an extensive section on the actual hardware of the system.

With the nuclear detente following the collapse of the Soviet Empire, some experts question the region from whence the potential threat of ballistic missile attack emanates. North Korea, for example, has a long history of illicit ballistic missile development, and related connections to nations like Pakistan and Iran.