目前擁有核武的國家可以分為兩大類：「公認的核武國家」與「未經承認但實際擁有核武的國家」。這樣的區分來自於一個關鍵性的國際條約——《不擴散核武器條約》（Nuclear Non-Proliferation Treaty, NPT）。

根據這個條約，世界上只有五個國家被「合法」認定擁有核武，它們是：美國、俄羅斯、英國、法國與中國。這五個國家都是在1967年1月1日之前就成功研發並試爆核武器的，因此在NPT中被視為「核武國家」（Nuclear-Weapon States, NWS）。這種「合法性」其實是一種政治妥協，並不代表國際社會真正認可核武的正當性，而是基於現實條件下為防止更多國家擴散核武所達成的規範。

然而，除了上述五國，還有幾個國家「未加入NPT」或「違反NPT條款」而自行發展核武。這些國家包括：印度、巴基斯坦、以色列和北韓。其中，印度與巴基斯坦從未加入NPT，並在1998年互相試爆核彈，成為南亞的核對峙雙雄；以色列則從未公開承認擁核，但外界普遍相信其擁有數十枚核彈，是一種「戰略模糊」的政策；至於北韓，則是2003年退出NPT，隨後進行多次核試，成為全球安全最大的變數之一。

這些「非法」或「不受承認」的核武持有國，往往受到國際制裁、外交壓力，甚至在地緣政治上遭遇孤立。不過，國際社會對這些國家的核武問題處理上，往往也充滿現實主義與選擇性標準，例如對以色列的態度就明顯寬容，對北韓則極度嚴厲。

至於製造原子彈的難度，從理論與技術層面來說，實際上在1940年代末期之後已非難事。曼哈頓計畫結束後，許多技術與設計逐漸解密，加上現代電腦模擬與全球科研知識共享，想要「知道如何做出原子彈」其實並不難。真正的瓶頸在於材料，特別是高濃縮鈾（U-235）與武器級鈽（Pu-239）的取得與提煉。

天然鈾含量中，U-235只佔約0.7%，要用來製造核武，必須提純至90%以上，而這需要高端的離心機系統或氣體擴散設施。這種技術門檻不僅高，還極度耗能與昂貴。許多國家即使有技術，沒有足夠的資源與政治決心，也很難跨越這道門檻。同時，國際原子能機構（IAEA）會對全球各核設施進行監控與稽查，一旦某國企圖濃縮鈾到武器級，往往會被偵測與制裁。

因此，真正能躋身核武俱樂部的國家，往往不是因為技術有多高超，而是因為有政治決心、戰略需求、國內資源，以及能承受國際壓力的能力。核武，從來不只是科學問題，更是國際權力與秩序的象徵。

Countries Currently Possessing Nuclear Weapons Can Be Divided into Two Main Categories: “Recognized Nuclear States” and “Unacknowledged but De Facto Nuclear Powers.”

This distinction originates from a pivotal international treaty—the Nuclear Non-Proliferation Treaty (NPT).
According to the NPT, only five countries in the world are “legally” recognized as possessing nuclear weapons: the United States, Russia, the United Kingdom, France, and China. These five nations had successfully developed and tested nuclear weapons before January 1, 1967, and are thus considered Nuclear-Weapon States (NWS) under the treaty. This “legitimacy” is essentially a political compromise, not a moral endorsement of nuclear arms. It reflects a practical attempt to prevent further nuclear proliferation rather than a universal approval of nuclear weapons.

However, beyond these five, several other countries have developed nuclear capabilities either without joining the NPT or by violating its terms. These include India, Pakistan, Israel, and North Korea.India and Pakistan have never signed the NPT and conducted tit-for-tat nuclear tests in 1998, establishing a nuclear standoff in South Asia. Israel has never officially acknowledged possessing nuclear weapons, but it is widely believed to have dozens of warheads, a posture known as “strategic ambiguity.” North Korea, on the other hand, withdrew from the NPT in 2003, and has since carried out multiple nuclear tests, becoming one of the most volatile threats to global security.

These “illegal” or “unrecognized” nuclear-armed states are often subject to international sanctions, diplomatic pressure, and geopolitical isolation. However, the global response to these nations is often inconsistent and driven by realism. For instance, Israel is treated with relative leniency, while North Korea faces extreme scrutiny and condemnation.

As for the technical difficulty of building an atomic bomb, it has not been a major obstacle since the late 1940s. After the end of the Manhattan Project, much of the technology and design principles gradually became declassified. With modern computer simulations and the global sharing of scientific knowledge, “knowing how to build a bomb” is no longer the main challenge. The real bottleneck lies in acquiring the necessary materials, especially highly enriched uranium (U-235) and weapons-grade plutonium (Pu-239).

Natural uranium contains only about 0.7% U-235, but for use in a nuclear weapon, this needs to be enriched to over 90%. Achieving this requires advanced centrifuge systems or gaseous diffusion facilities—technologies that are not only highly sophisticated but also extremely energy-intensive and costly. Even countries with the technical know-how often lack the resources or political will to cross this threshold. Furthermore, the International Atomic Energy Agency (IAEA) monitors and inspects nuclear facilities worldwide. Any attempt by a nation to enrich uranium to weapons-grade levels is likely to be detected and result in sanctions.

Therefore, the ability to join the nuclear weapons club is not just a matter of technical prowess—it depends heavily on political determination, strategic necessity, domestic resources, and the capacity to withstand international pressure.
Nuclear weapons have never merely been a scientific issue—they are, above all, a symbol of international power and order.