Question: What year did the country where Siddhi Savetsila was born form an alliance with Japan?

Knowledge 1: Siddhi Savetsila
Siddhi Savetsila was born in Bangkok. He comes from an aristocratic background. His father was a high-ranking official in the royal government. His paternal grandfather was Henry Alabaster who was the British consul in Siam during the reign of King Rama IV (Mongkut) and then served as an advisor to King Rama V (Chulalongkorn). His mother was an offspring of the influential Bunnag family, the daughter of Thet Bunnag (later Chao Phraya Suraphan Phisut), making him a direct descendant of Somdet Chao Phraya Borom Maha Prayurawongse. [SEP] Knowledge 2: Pacific War
The Axis states which assisted Japan included the authoritarian government of Thailand in World War II, which quickly formed a temporary alliance with the Japanese in 1941, as the Japanese forces were already invading the peninsula of southern Thailand. The Phayap Army sent troops to invade and occupy northeastern Burma, which was former Thai territory that had been annexed by Britain much earlier. Also involved were the Japanese puppet states of Manchukuo and Mengjiang (consisting of most of Manchuria and parts of Inner Mongolia respectively), and the collaborationist Wang Jingwei regime (which controlled the coastal regions of China). [SEP] Knowledge 3: Bang Bon District
Bang Bon (Thai: บางบอน, pronounced [bāːŋ bɔ̄ːn]) is one of the 50 districts (khet) of Bangkok, Thailand. Its neighbours, clockwise from north, are Bang Khae, Phasi Charoen, Chom Thong, and Bang Khun Thian districts of Bangkok, Mueang Samut Sakhon District and Krathum Baen District of Samut Sakhon Province, and Nong Khaem District of Bangkok.
Knowledge 1: Siddhi Savetsila
Siddhi Savetsila was born in Bangkok. He comes from an aristocratic background. His father was a high-ranking official in the royal government. His paternal grandfather was Henry Alabaster who was the British consul in Siam during the reign of King Rama IV (Mongkut) and then served as an advisor to King Rama V (Chulalongkorn). His mother was an offspring of the influential Bunnag family, the daughter of Thet Bunnag (later Chao Phraya Suraphan Phisut), making him a direct descendant of Somdet Chao Phraya Borom Maha Prayurawongse. [SEP] Knowledge 2: Imperialism
During the First Sino-Japanese War in 1894, Japan absorbed Taiwan. As a result of the Russo-Japanese War in 1905, Japan took part of Sakhalin Island from Russia. Korea was annexed in 1910. During World War I, Japan took German-leased territories in China’s Shandong Province, as well as the Mariana, Caroline, and Marshall Islands. In 1918, Japan occupied parts of far eastern Russia and parts of eastern Siberia as a participant in the Siberian Intervention. In 1931 Japan conquered Manchuria from China. During the Second Sino-Japanese War in 1937, Japan's military invaded central China and by the end of the Pacific War, Japan had conquered much of the Far East, including Hong Kong, Vietnam, Cambodia, Myanmar, the Philippines, Indonesia, part of New Guinea and some islands of the Pacific Ocean. Japan also invaded Thailand, pressuring the country into a Thai/Japanese alliance. Its colonial ambitions were ended by the victory of the United States in the Second World War and the following treaties which remanded those territories to American administration or their original owners. [SEP] Knowledge 3: Bang Bon District
Bang Bon (Thai: บางบอน, pronounced [bāːŋ bɔ̄ːn]) is one of the 50 districts (khet) of Bangkok, Thailand. Its neighbours, clockwise from north, are Bang Khae, Phasi Charoen, Chom Thong, and Bang Khun Thian districts of Bangkok, Mueang Samut Sakhon District and Krathum Baen District of Samut Sakhon Province, and Nong Khaem District of Bangkok.
Knowledge 1: Siddhi Savetsila
Siddhi Savetsila was born in Bangkok. He comes from an aristocratic background. His father was a high-ranking official in the royal government. His paternal grandfather was Henry Alabaster who was the British consul in Siam during the reign of King Rama IV (Mongkut) and then served as an advisor to King Rama V (Chulalongkorn). His mother was an offspring of the influential Bunnag family, the daughter of Thet Bunnag (later Chao Phraya Suraphan Phisut), making him a direct descendant of Somdet Chao Phraya Borom Maha Prayurawongse. [SEP] Knowledge 2: Bang Bon District
Bang Bon (Thai: บางบอน, pronounced [bāːŋ bɔ̄ːn]) is one of the 50 districts (khet) of Bangkok, Thailand. Its neighbours, clockwise from north, are Bang Khae, Phasi Charoen, Chom Thong, and Bang Khun Thian districts of Bangkok, Mueang Samut Sakhon District and Krathum Baen District of Samut Sakhon Province, and Nong Khaem District of Bangkok. [SEP] Knowledge 3: Pacific War
In September 1940, Japan decided to cut China's only land line to the outside world by seizing Indochina, which was controlled at the time by Vichy France. Japanese forces broke their agreement with the Vichy administration and fighting broke out, ending in a Japanese victory. On 27 September Japan signed a military alliance with Germany and Italy, becoming one of the three Axis Powers. In practice, there was little coordination between Japan and Germany until 1944, by which time the U.S. was deciphering their secret diplomatic correspondence.

Answer: 1941