The overlapping power transitions in East Asia's three main economies promise to mark a defining moment in the region's tense geopolitics and compound America's diplomatic challenges.
After the ascension in China of Xi Jinping, regarded by the People's Liberation Army (PLA) as its own man, Japan's swing to the right in its parliamentary election is set to fuel nationalist passion on both sides of the Sino-Japanese rivalry just when their territorial spat in the East China Sea has created new risks to regional peace and stability. Shinzo Abe, a hawk on China, will take over as Japan's new prime minister the day after Christmas.
South Korea's presidential election swept another conservative to power in succession, but one who supports conditional rapprochement with North Korea -- a line at variance with the current policies of departing President Lee Myung-bak and President Obama to keep Pyongyang punitively isolated. Park Geun-hye, the first woman to be elected president in a country that ranks poorly in gender equality, says she intends to tread the middle path between unconditional engagement and uncompromising chastisement.
Ms. Park, the unmarried 60-year-old daughter of South Korea's former military dictator, who ruled from 1961 to 1979, will assume the presidency in February.
In Japan, popular discontent over the failure of successive governments to stem two decades of economic stagnation, address the potential threat to public safety from another Fukushima-type nuclear disaster, and rein in China's increasingly muscular approach to territorial and historical issues has produced an insatiable hunger for change. Only three years after kicking out the conservative Liberal Democratic Party (LDP) in a historic vote that ended its nearly uninterrupted hold on power for 54 years, voters have brought the old guard back to office by ousting the left-leaning Democratic Party of Japan (DPJ).
These political transitions could exacerbate East Asia's challenges, which include the need to institute a regional balance of power and dispense with historical baggage that weighs down interstate relationships. Booming trade in the region has failed to mute or moderate territorial and other disputes. On the contrary, it has only sharpened regional geopolitics and unleashed high-stakes brinkmanship. Economic interdependence cannot deliver regional stability unless rival states undertake genuine efforts to mend their political relations.
The timing of the political transitions is particularly problematic for the Obama administration, which has been urging China and Japan to peacefully resolve their disputes. It has, at the same time, sought to build closer strategic cooperation between its two allies, South Korea and Japan, and keep the Stalinist regime in North Korea under stringent sanctions.
After South Korea's Mr. Lee came to office in February 2008, he reversed South Korea's decade-long "sunshine policy" toward North Korea, choosing to cut off bilateral aid and step up pressure on Pyongyang. That, in turn, prompted the North to scale back inter-Korean contact, carry out provocative actions, including missile tests, and ratchet up bellicose rhetoric. Relations between the two Koreas sunk to a low in 2010 following the death of 46 South Korean sailors in the sinking of a warship -- blamed on a North Korean torpedo attack -- and the North's shelling of the South's Yeonpyeong Island.
Despite Pyongyang's successful rocket launch last week in defiance of United Nations Security Council resolutions, Mr. Lee's successor, Ms. Park, has promised to allow humanitarian aid to the North and try to hold talks with its young leader Kim Jong-un, who came to power a year ago following the death of his father, Kim Jong-il. Ms. Park's more moderate approach could undercut the Obama administration's North Korean policy just when Pyongyang has signaled open defiance of international pressure.
Despite Washington's efforts, the new strains in South Korea's relationship with Japan, owing to the revival of historical issues, may be difficult to mend. Earlier this year, Mr. Lee, at the last minute, canceled the scheduled signing of a General Security of Military Information Agreement with Japan, which would have established military intelligence-sharing between the two countries for the first time. He also scrapped a bilateral plan to finalize a military-related Acquisition and Cross-Servicing Agreement. Weeks later, he provocatively visited the contested islets known as the Dokdo Islands in South Korea (which controls them) and the Takeshima Islands in Japan.
Ms. Park may also seek to pander to nationalist sentiment at home by taking a tough stance against Japan, especially to play down her father's collaboration with the Japanese military while Korea was under Japanese colonial rule.
China, meanwhile, has launched a new war of attrition against Japan over the Senkaku Islands, which China calls Diaoyu. By sending patrol ships frequently to the waters around the islands since September -- and violating airspace over them recently -- Beijing has sought to challenge Japan's decades-old control over them, despite the risk that an incident at sea or in the air between the two sides could spiral out of control.
This physical assertiveness followed often-violent anti-Japanese protests in China in September, while a continuing informal boycott of Japanese goods has led to a sharp fall in Japan's exports to China, raising the risk of another Japanese recession. China, after all, is Japan's largest overseas market.
China's behavior has fueled a nationalist backlash in Japan, which is only fanning Chinese nationalism, creating a vicious circle from which the two countries are finding it difficult to escape.
The risks posed by increasing nationalism and militarism to peace in East Asia have already been highlighted by the rise of a new Chinese dynasty of "princelings," or sons of revolutionary heroes, who have widespread contacts in the military. In fact, what distinguishes Mr. Xi from China's other civilian leaders is his strong relationship with the PLA, whose rising clout has underpinned China's increasingly assertive foreign policy.
Against this background, the central challenge for East Asian countries is to resolve the historical issues that are preventing them from charting a more stable and prosperous future.
Brahma Chellaney, professor of strategic studies at the Center for Policy Research in New Delhi, is the author of "Water: Asia's New Battleground" (Georgetown University Press, 2011).