Japanese decision for war in 1941
While the Empire of Japan was largely committed to forcible expansion by the late 1930s, specific plans, decisions and preliminary operations (e.g. French Indochina), by the Empire of Japan, were made to begin large-scale operations of World War Two in the Pacific in December 1941, primarily in 1941 but some in 1940. These wre more detailed than broad strategic directions such as the Strike-North and Strike-South Factions, or a decision to consolidate in China and Manchuria.
The decision to go to war, however, is rarely completely rational. In a 2009 paper, Jeffrey Record, of the U.S. Air War College, observes a number of points that led to Japan's decision, and are lessons not to be forgotten by future policymakers:
- Fear and honor, “rational” or not, can motivate as much as interest.
- There is no substitute for knowledge of a potential adversary’s history and culture.
- Deterrence lies in the mind of the deterree, nott he deterrer.
- Strategy must always inform and guide operations.
- Economic sanctioning can be tantamount to an act of war.
- The presumption of moral or spiritual superiority can fatally discount the consequences of an enemy’s material superiority.
- “Inevitable” war easily becomes a self-fulfilling prophesy.
Who were the enemies?
Originally, the Strike-South was to have been of moderate scope, confronting only Britain. This soon expanded, though, to an inevitable confrontation with the Netherlands over Indonesia (then the Dutch East Indies). Confrontation with Australia and the United States were more complex. Japan never had serious intent to invade Australia, but recognized that Australia would be threatened by nearby activities and indeed might compete for some of the same resources. If Japan attack the Philippines, that would be a direct attack on a U.S. territory, but, even if Japan did not, there was the danger that the U.S. would support its Western allies.
To what extent Japan understood it is unclear, but Franklin D. Roosevelt saw anything that interfered with Britain's ability to fight Nazi Germany as of vital strategic interest to the U.S. Malaya and Singapore provided Britain with essential resources.
The situation with France also was complex, as Japan saw Vichy as an ally. Operations in French Indochina, taken in 1940, were transitional, in that they directly bore on the Second Sino-Japanese War, but also would establish bases for Strike-South. Strike-North had largely been rejected due to the rough handling of Japanese troops, by Soviet forces, on the border, including such things as the Nomohan Incident.
Prince Saionji would normally recommended the new Prime Minister, after the fall of Hirota govenrment, but was reluctant to come to the Palace. Told he would not to have to travel to Tokyo. Saionji immediately recommended General Kazushige Ugaki, "who, as Governor General of Korea, had made himself the leader of the army officers who took a moderate position between the Strike North and Strike Suth Factios. He had he support of the political parties and the carrels. Most important, he was outspoken in his opposition to the planned war of aggtession in China. Ugaki did not want the job, and reigned from the resarve. On January 29, Hirohiro convinced him to keep his commission, and be foreign minister in the cabinet after nextt. 
1940 and Konoe
After preparatory meetings, Prince Konoe was authorized, on 17 July 1940 by Hirohito, to form a cabinet. In a meeting six days before, he had gained the support of President of the Privy Council Yoshimichi Hara, as well as four other prior prime ministers, Senjuro Hayashi, Koki Hirota, Keisuke Okada and Reijiro Watasuki. His cabinet succeeded that of Mitsumasu Yonai.
apan hoped, especially after the fall of France, to work diplomatically with Vichy France, even before the Tripartite Pact was signed, both to cut off supplies to Chiang Kai-Shek and to establish airbases in French Indochina, needed to strike further south and east.
Georges Catroux, French governor of Indochina, did close the border with China. A Japanese verification group, headed by Major General Issaku Nishimura entered Indochina on June 25. On the same day that Nishimura arrived, Vichy dismissed Catroux, for independent foreign contact. He was replaced by Vice Admiral Jean Decoux, who commanded French naval forces in the Far East, and was based in Saigon. Ducoux and Catroux were in general agreement about policy, and considered managing Nakamura the first priority.  Ducoux had additional worries. The senior British admiral in the area, on the way from Hong Kong to Singapore, visited Ducoux and told him that he might be ordered to sink Ducoux's flagship, with the implicit suggestion that Ducoux could save his ships by taking them to Singapore, which appalled Ducoux. While the British had not yet attacked French ships that would not go to the side of the Allies, that would happen at Mers-el-Kabir in North Africa within two weeks; it is not known if that was suggested to, or suspected by, Ducoux. Deliberately delaying, Ducoux did not arrive in Hanoi until July 20, while Catroux stalled Nishimura on basing negotiations, also asking for U.S. help. 
- Jeffrey Record (February 2009), Japan's Decision for War in 1941: Some Enduring Lessons, Strategic Studies Institute, U.S. Army War College, p. ix
- David Bergamini (1971), Japan's Imperial Conspiracy, Morrow p. 679-680
- Herbert P. Bix (2001), Hirohito and the making of modern Japan, Harper Perennial, ISBN 978-0060931308, pp. 373-374
- Merion and Susie Harris (1991), Soldiers of the Sun: the Rise and Fall of the Imperial Japanese Army, Random House, pp. 275-276
- Arthur J. Dommen (2001), The Indochinese Experience of the French and the Americans, Indiana University Press pp. 47
- Martin Gilbert (1989), The Second World War, Stoddart, p. 107
- Dommen, p. 48