The Asia-Pacific geopolitical context is rapidly evolving, and nowhere more so than Northeast Asia. China’s economic rise has helped to drive higher levels of prosperity throughout Asia, resulting in far greater ambitions for its future role as a regional and global power. Neighboring countries are now caught in a delicate balancing act between the US and China as they vie for dominance. Meanwhile, rising tensions over Taiwan and an increasingly bellicose and nuclear-capable North Korea darken the regional security picture. Against this backdrop, the traditionally complex relationship between Japan and South Korea is entering a new, more collaborative phase. What impact will these shifting regional dynamics have on security cooperation among US-allied states in the Indo-Pacific or on China’s defense posturing? Will growing security considerations force an adjustment of trade and investment policies?