In 2012, the United States declared pivot to Asia-Pacific strategy, which has begun to reshape overall geostrategic landscape in the region. After the U.S. readjusted its global posture and shifted its major naval and air forces to Pacific theater, China subsequently adopted a series of counter actions, including East China Sea Air Defense Identification Zone and fishing reporting requirement in South China Sea. China's proactive attitude is completely different from what it has done in last several decades. The study will review, based on neo-realism and historical sea power and land power struggle precedence in Thucydides, the impact of these developments to regional countries, how regional countries adapt to changing environment and secure their national interests and what shall the Republic of China consider under this circumstance.