The Greater East Asian Co-Prosperity Sphere was an Imperial Japanese political and military concept, developed around 1931. In this concept, lay the blueprint for Japan's ''Global Expansion'' and establishment as a ''World Power''. The Plan also was seen as the beginnings of World War II in The Pacific Region.
The ideology was simple. Japan saw that it was necessary to ''unite'' all Asian Nations together for economic and political ''security''. Naturally, as ''One Nation'' – Imperial Japan was selected by ''Divine Right'' to lead such. Japan began a campaign of Military conquests to insure that their ideology was advanced. They moved into Northern China, Korea and many smaller South Pacific Islands and Independent Territories. Occupying such, they began a systematic plan of subjugation (torture and murder) – to remove any resistance.
Political Propaganda was still the favored method of conversion (for Japan had limited Military resources). Often, espionage was the the final solution to those more ''stubborn'' Nations. Once a ''Puppet Government'' was established, The ''Sphere'' advanced. The United States and Great Britain were the few Countries that attempted to curb Japan's advances. Seen for what The ''Sphere'' really was – Thousands of British Soldiers (already garrisoning many Colonial Territories), tried to stem Japan's movements, without starting a War. The US too, began to heavily garrison and deploy it's Navy to The South Pacific (in a show of continuous force).
However, both Countries were ''hamstrung'' by The Washington Naval Treaty of 1922. The Treaty, signed with most European Nations which maintained a Naval Service – was designed to limited the overall size and Vessel type, which a Nation could have. This Treaty was designed to limit the lessons learned in the last ''War to End All Wars'' (WWI). While Japan was a signatory, She still (as did Germany and Italy) – secretly build Ships and weapons that were against Treaty Rules. No one was ''really paying attention''. When proof of this violation reached The US, the majority of Japan's Oil Imports (from The US), was cut off. As such, Japan's Navy was placed into a critical position. This position would spur the Japanese decision to attack Pearl Harbor on December 7, 1941 (after Japan had gotten a firm grasp on The Pacific).
The so-called ''Sphere'' (after the start of World War II), begin to falter, as both The US and Britain supported revolts and resistance within most of Japan's Territories. A series of important military victories would find The Great East Asian Co-Prosperity Sphere ''smashed'' in August of 1945, when Imperial Japan surrendered to The Allies – ending World War II.