The Korean peninsula is evolving into an acute security concern for Japan, with a host of provocations this year.

U.S. President Barack Obama's policy of strategic patience with regard to the North has failed, and Pyongyang has continued to expand its capabilities in missile technology and weapons of mass destruction. Since the beginning of the year, the North has conducted two nuclear weapons tests and a barrage of ballistic missile tests aimed at refining range and accuracy.

Continued instability in the peninsula will be one of the chief international security problems that Obama's successor will inherit when he or she takes office next year. Adding to this problem is concern among U.S. allies — including Japan — about the credibility of Washington's treaty commitments across the region.

U.S. presidential candidate Donald Trump has questioned the value of U.S. alliances with Tokyo and Seoul, accusing both countries of engaging in free-riding and benefiting from Washington's security guarantees at little cost to themselves. Trump also has suggested that Japan and South Korea should look to the procurement of nuclear weapons as a potential solution to regional security threats posed by North Korea.

Click here to read the full article in Nikkei Asian Review.