N.Korea and S.Korea: North Korea will collapses within 10 years due to covert regime change by the US and Japan or the murder of Kim Jong Il by his own military after he fails to be able to bribe them effectively.
This will result in refugees flooding into a South Korea economically unable to provide for all of them and into China. The new united but poor Korea will have nuclear weapons and become increasingly nationalist and xenophobic, which will drastically destabilize its relationship with the United States and especially with Japan. Korean refugees in China will become a small, despite its redcurrant nationalism, Korea will slowly and continually slip under the Chinese sphere of influence as its economy becomes even more dependent on
Japan: Under American pressure and public pressure over instability on the Korea Peninsula and fear of a powerful China, Japan will remilitarize which will aggravate its relations with both Koreas and China to a lesser extent. Part of this remilitarization will be a slow move to Japan going “nuclear” which will take place within 10 years of Japan changing its “peace constitution.” Nationalism at this time and anti-Asia neighbor sentiment will rise as a reaction to perceived unfairness by its Asian neighbors over WWII and rallying of the public by the right wing. This nationalism will create an unexpected strain between America and Japan who will remain close allies against China, but also have both having strong economic interest in China, as well as similar security interest in the region. The American military presence will be decrease in Japan as Japanese forces take a lead role. Despite the increase in nationalism, there will be a strong pro-China lobby forming, because historically Japan always seeks to make alliances and mimic the nations that it views as the strongest, many, at least from a regional perspective, begin to see China as a revived power in the region to seriously rival China.
China and Taiwan: Taiwan will not declare formal independence, instead it will form a type of federation (similar to that with between Hong Kong SAR and Mainland China, but with even more leeway given to Taiwan) for an indefinite period. This will avoid a war between Japan, America, and China over Taiwanese independence, where America and Japan will attempt to defend Taiwan militarily. China being capable of bombing Taiwan but not holding the island will be willing to avoid war unless Taiwan declares formal independence because a loss of Taiwan after a military conflict will cause the government to lose face, but also allowing Taiwan to formally succeed with no military response will be a worse loss of face, both likely resulting in internal pressure from home leading to serious uprisings that could topple the CCP, especially considering any military action will likely severely hurt China’s economy already aggravating the gap between rich and poor, rural and urban. This will be seen as victory for China by many right wing hawks in Japan and America.
Vietnam: Vietnam is included because it is culturally more an East Asian nation than a Southeast Asian due to its extensive historical contact with China. Vietnam will seek to balance China’s political and economic power in the region by establishing closer bilateral relations with the United States and becoming a more active promoter of ASEAN, as a negotiating device giving it more power in its relationship with China and the other East Asian nations. China will put more pressure on a United Korea to get military distance from America and even help promote Korean nationalism.
United States: Will lose all of its bases in the new united Korea and most of them in Japan although there will be a lose military alliance with the new militarized Japan, but over time Japan will slowly move back into China’s political orbit, but due to issues with Korea will remain some counterbalance with America out of fear. America will increasingly try to balance its economic issues with China and its fear of Chinese political power, not just in Asia, but increasingly its global political power, that often conflicts with U.S. interests.
ASEAN: China and Korea will join a new East Asian trade group born out of ASEAN, eventually, within 20 years time Japan will have no choice but to also join although hesitantly fearing Chinese domination. ASEAN itself will morph into an East-South East Asian trade group, much more diversified and less powerful than the EU, and dominated largely by China and Japan…which will form two balancing rival poles in the organization with small nations choosing sides. America will be excluded from this group causing some animosity and fear of Chinese power. Japan will (secretly) serve to help promote US economic interests.