Since sweeping to power in May 2014 in India's biggest election victory in a generation, Prime Minister Narendra Modi has made his impact more in diplomacy than in domestic policy, a realm where he faces a core challenge similar to that of his Japanese counterpart and ideological soul mate, Shinzo Abe — to lead his country toward greater economic and military security.

Modi, like Abe, has surprised many by investing considerable political capital in high-powered diplomacy. But Modi, a provincial leader, came to office, unlike Abe, with little foreign policy experience. In recent months, foreign leaders have made a beeline to call on Modi — ranging from Chinese President Xi Jinping to U.S. President Barack Obama, who will be the guest of honor at India's Jan. 26 Republic Day parade, a year after Abe had that privilege.

Modi, after hosting Russian President Vladimir Putin in December, is preparing to receive Obama at a time when U.S.-led sanctions against Moscow have underscored the risks of a new Cold War. No American president before was the chief guest at India's Republic Day.