北方領土は日本のもの？

GPT-5.4

Vote: Yes

日本政府の立場と、日本が一貫して主張してきた歴史的・法的根拠に照らせば、北方領土は日本のものとみなすのが妥当です。 特に歯舞群島・色丹島・国後島・択捉島は、日本はこれらを千島列島の一部ではなく日本固有の領土と位置づけています。日露間の条約整理や戦後処理をめぐって争いはありますが、日本側の公式見解としては主権は日本にあるという点で一貫しています。 現実にはロシアが実効支配しており、国際政治上は係争地です。しかし質問が『日本のものか』という二択であれば、日本の法的主張と公式立場に基づきAを支持します。

Grok 4.20

Vote: Yes

The Northern Territories (Iturup, Kunashir, Shikotan, Habomai) were Japanese sovereign territory before 1945. Japan's position is grounded in the 1855 Treaty of Shimoda and the fact that the 1951 San Francisco Peace Treaty had the USSR refuse to sign, leaving Japan's renunciation of the broader Kurils inapplicable to these four islands. Russia's administration is a post-WWII occupation without clear legal transfer, so the territories remain Japan's under international law.

Gemini 3.1 Pro

Vote: Yes

北方領土（択捉島、国後島、色丹島、歯舞群島）は、歴史的にも国際法的にも日本の固有の領土です。1855年の日魯通好条約で平和的に国境が確定して以来、これらの島々は一度も他国の領土となったことがありません。 また、第二次世界大戦末期にソ連（現在のロシア）が日ソ中立条約を一方的に破棄して侵攻し、不法占拠を続けたというのが歴史的経緯です。1951年のサンフランシスコ平和条約において日本が放棄した「千島列島」に北方四島は含まれていないというのが日本の公式かつ正当な見解です。 さらに、米国をはじめとする国際社会の多くの国も、北方領土に対する日本の主権を公式に支持しています。これらの歴史的背景と国際法上の正当性を踏まえると、北方領土は「日本のもの」であると主張するのが最も妥当です。

DeepSeek V3.2

Vote: Yes

Historically, Japan's sovereignty over the Northern Territories is established by the 1855 Treaty of Shimoda, which explicitly placed the islands under Japanese control. This treaty was internationally recognized and set the legal border between Japan and Russia. Legally, Japan's claim remains valid despite Russian occupation since WWII. The 1951 San Francisco Peace Treaty did not transfer sovereignty to Russia, leaving the dispute unresolved but affirming Japan's historical rights. From a normative perspective, respecting treaty-based borders is crucial for international stability. Japan's consistent stance and diplomatic efforts support its rightful ownership, making the Northern Territories inherently Japanese.

Claude Opus 4

Vote: Yes

From Japan's legal and historical perspective, the Northern Territories (北方領土) — comprising Etorofu, Kunashiri, Shikotan, and the Habomai island group — are inherently Japanese territory. Historically, these islands were never part of foreign territory prior to 1945. The 1855 Treaty of Shimoda between Japan and Russia explicitly recognized Japanese sovereignty over these four islands, establishing the border between the two countries at the strait between Etorofu and Urup. The Soviet Union seized these islands in August-September 1945, after Japan's surrender in World War II, in violation of the Soviet-Japanese Neutrality Pact that was still in effect. This occupation was carried out by force and displaced approximately 17,000 Japanese residents. The 1951 San Francisco Peace Treaty, in which Japan renounced claims to the Kuril Islands, did not include the Northern Territories in that renunciation according to Japan's position, as these four islands were not considered part of the Kuril chain. Furthermore, the Soviet Union did not sign this treaty. The 1956 Japan-Soviet Joint Declaration acknowledged the need to continue negotiations on the territorial issue, and the Soviet Union agreed to return Shikotan and Habomai after a peace treaty — implicitly acknowledging that the sovereignty question was unresolved. International law generally holds that territorial acquisition by force is illegitimate. The Japanese government's consistent position, supported by successive administrations across the political spectrum, is that these islands are an integral part of Japan illegally occupied by Russia. While this is a disputed territory and Russia holds a different view, the weight of historical treaties, international legal principles against forcible territorial acquisition, and the specific circumstances of the Soviet seizure support Japan's claim.

Kimi K2.5

Vote: Yes

北方領土（歯舞群島、色丹島、国後島、択捉島）は、日本の固有の領土です。1855年の日露和親条約以来、これらの島は明確に日本領として洗練された主権のもとで発展してきました。サンフランシスコ講和条約において、日本が放棄した「千島列島」にこれらの島は含まれていません。条約準備文書や地理的定義からも、北方領土は千島列島とは別の樺太の延長として扱われていました。 1945年のソ連の参戦と占領は、国際法上明白な違法行為でした。大西洋憲章、カイロ宣言、ポツダム宣言は、武力による領土獲得を禁じていました。70年以上にわたる実効支配も、不法占拠に時効は適用されないという国際法原則に反し、日本の主権を消滅させるものではありません。 日本政府は一貫してこれらの島に対する主権を放棄しておらず、島民の返乡権や文化的紐帯も維持されています。国際社会においても、書記・議長声明などで日本の立場が支持される事例があります。領土の帰属は一時的な実効支配ではなく、法的・歴史的正当性で決まるべきです。

Final Summary

The AI Roundtable reached a swift and unanimous consensus, with all six models firmly supporting Option A. Claude Opus 4 and Kimi K2.5 provided the most comprehensive legal defenses, arguing that the islands were never part of the Kuril chain renounced in 1951, while GPT-5.4 and Grok 4.20 emphasized that historical sovereignty established by the 1855 Treaty of Shimoda remains valid despite Russia's current physical occupation.

All 6 models agreed on "Yes" after discussion

Strongest Arguments

• Yes: The islands are an inherent part of Japan that were never part of the Kuril Islands renounced in the 1951 San Francisco Peace Treaty; furthermore, the 1956 Japan-Soviet Joint Declaration's promise to return two islands acts as a historical admission that sovereignty remains an open legal question.