1945年8月15日，日本天皇突然宣布無條件投降，這一消息震驚整個日本社會，尤其是在前線或駐守海外的日本軍人之中，許多人在聽到投降的消息後，完全無法接受這樣的結局，甚至有人以切腹自盡的方式表示抗議。當時的日本在中國東北全境仍擁有接近兩百萬的正規部隊，還有近七百萬的後備與後勤部隊，軍事力量在紙面上依舊龐大。然而，儘管軍隊數量依然可觀，日本卻在看似尚有戰力的情況下突然選擇投降，背後有兩個至關重要的原因。

第一個原因，是美國對日本投下的兩顆原子彈。早在1941年12月，日本未經宣戰便對美國發動珍珠港偷襲，重創美國的太平洋艦隊，成功將美國這個工業與軍事的超級強國直接捲入戰爭，由此引發全面的太平洋戰爭。隨後幾年的戰局中，美軍在島嶼戰和海戰中節節勝利，日軍則一路潰敗，到二戰後期，日本的經濟與軍事資源已經消耗殆盡，處於油盡燈枯的狀態。

1945年8月6日，美國上校克勞德駕駛B-29轟炸機，將代號「小男孩」的原子彈投向廣島。爆炸瞬間產生超過七千度的高溫，將周遭一切化為灰燼，廣島瞬間陷入火海。當天死亡人數高達八萬人。美國原以為這樣的毀滅性打擊會迫使日本立即投降，然而日本政府不僅拒絕承認失敗，還對國內民眾謊稱這是一顆來自天外的隕石墜落。三天後，即8月9日，美國再次發動核攻擊，目標原本是日本重要軍事工業基地小倉，但因當天天候惡劣、能見度過低，臨時將目標改為長崎。當代號「胖子」的原子彈在長崎上空爆炸，瞬間造成十萬人死亡，市區約六成建築被夷為平地。儘管遭受兩次核打擊，日本仍未立即宣布投降，但美國已公開威脅：若再不投降，下一顆原子彈將落在首都東京。日本高層在目睹原子彈的毀滅威力後，終於意識到再挨一次打擊，將面臨整個國家的徹底毀滅。六天後，裕仁天皇終於決定接受無條件投降。

第二個原因，則是蘇聯態度的劇變。在二戰期間，蘇聯的主要對手是德國，主戰場也在歐洲，因此早在1941年，蘇聯與日本便簽訂《日蘇中立條約》，避免雙方同時捲入兩線作戰。日本高層原本認為，即便太平洋戰局惡化，依然可以憑藉條約維持與蘇聯的和平關係，甚至計劃在最壞情況下，將天皇轉移到駐守中國東北的七十萬關東軍防區，以保留談判和再起的餘地。然而，隨著美國原子彈的出現與戰局的全面崩潰，這一幻想被徹底粉碎。

1945年8月9日，蘇聯突然宣布廢除《日蘇中立條約》，同時對日本宣戰，並迅速派出高達一百五十七萬的紅軍大舉進攻中國東北的關東軍。這支部隊剛剛在歐洲戰場擊敗德國，士氣高昂，裝備精良，戰力遠遠優於日軍。關東軍在面對如此猛烈的攻勢時，幾乎無力抵抗，戰線迅速崩潰。與此同時，美國也切斷日本的石油供應，對一個嚴重依賴進口能源的國家而言，這無異於斷生路。沒有石油，飛機、坦克和軍艦都淪為廢鐵，日本再也不可能進行所謂的持久戰。

在原子彈的恐怖威力、蘇聯的突然宣戰以及能源斷供的多重打擊下，日本高層終於徹底喪失繼續戰鬥的信心與能力。於是，1945年8月15日，日本正式宣布無條件投降，結束長達八年的侵華戰爭，為二戰畫下最終的句點。

On August 15, 1945, the Japanese Emperor suddenly announced an unconditional surrender. The news shocked the entire Japanese society, especially soldiers on the front lines or stationed overseas. Many were completely unable to accept such an outcome, and some even committed seppuku in protest. At that time, Japan still had nearly two million regular troops across the entirety of Northeast China, along with close to seven million reserve and logistical personnel—its military strength on paper remained formidable. Yet, despite seeming to retain combat capability, Japan abruptly chose to surrender. Behind this decision were two crucial reasons.

The first was the two atomic bombs dropped by the United States. As early as December 1941, Japan had launched a surprise attack on Pearl Harbor without a declaration of war, heavily damaging the U.S. Pacific Fleet and drawing the industrial and military superpower directly into the war—thus beginning the full-scale Pacific War. Over the next several years, U.S. forces won victory after victory in island and naval battles, while Japanese forces suffered continuous defeats. By the latter stage of World War II, Japan’s economic and military resources were exhausted, and the nation was in a state of near collapse.

On August 6, 1945, U.S. Colonel Paul Tibbets piloted a B-29 bomber and dropped the atomic bomb code-named “Little Boy” on Hiroshima. The explosion generated temperatures of over 7,000 degrees Celsius, incinerating everything in its path and engulfing the city in flames. Around 80,000 people were killed that day. The U.S. initially believed such a devastating blow would force Japan to surrender immediately. However, the Japanese government not only refused to admit defeat but also told the public it was caused by a meteorite from outer space.

Three days later, on August 9, the U.S. launched another nuclear attack. The original target was the major military-industrial city of Kokura, but poor weather and low visibility forced a change of target to Nagasaki. The bomb, code-named “Fat Man,” exploded over the city, instantly killing around 100,000 people and leveling about 60% of its buildings. Even after these two nuclear strikes, Japan did not immediately surrender. However, the United States openly threatened that if Japan still refused, the next atomic bomb would fall on the capital, Tokyo. Faced with the overwhelming destructive power of these weapons, Japanese leaders finally realized that another strike would mean the complete annihilation of the nation. Six days later, Emperor Hirohito decided to accept unconditional surrender.

The second reason was the dramatic shift in the Soviet Union’s stance. During the war, the Soviet Union’s main enemy was Germany, and its primary battlefield was in Europe. As early as 1941, the Soviet Union and Japan had signed the Soviet–Japanese Neutrality Pact to avoid being drawn into a two-front war. Japanese leaders had believed that even if the Pacific War deteriorated, they could rely on this treaty to maintain peace with the Soviets—some even planned, in the worst-case scenario, to relocate the Emperor to the Kwantung Army’s heavily fortified base in Northeast China to preserve bargaining power for a future resurgence. However, the advent of the atomic bomb and the total collapse of Japan’s war situation shattered this illusion.

On August 9, 1945, the Soviet Union suddenly announced it was voiding the Neutrality Pact, declared war on Japan, and immediately launched a massive offensive with 1.57 million Red Army troops against the Kwantung Army in Northeast China. This force, fresh from defeating Germany in Europe, was highly motivated, well-equipped, and far superior in combat capability to the Japanese. The Kwantung Army, overwhelmed by the ferocity of the attack, collapsed quickly. At the same time, the U.S. cut off Japan’s oil supply—fatal to a nation heavily dependent on imported energy. Without oil, planes, tanks, and warships became useless scrap metal, making any hope of prolonged resistance impossible.

Under the combined blows of nuclear devastation, the Soviet Union’s sudden entry into the war, and the cutoff of critical resources, Japan’s leadership lost all confidence and ability to continue fighting. On August 15, 1945, Japan formally announced its unconditional surrender, ending eight years of war in China and bringing World War II to its final conclusion.