India and Japan took their biggest steps yet to deepen strategic ties, and it's mostly thanks to China.

Indian Prime Minister Narendra Modi and Japanese counterpart Shinzo Abe reached a slew of agreements in New Delhi over the weekend that underscore how their personal chemistry is translating into ever-warmer economic, military and strategic ties. The steps are designed to ensure that the rise of China, the top trading partner for both nations, doesn't come at the expense of smaller economies in the region.

"Modi and Abe are telegraphing a striking message: We're taking this relationship to the next level, even at the risk of roiling China," said Michael Kugelman, senior associate at the Woodrow Wilson Center in Washington. "As close as these two countries are, they had held off to an extent in order not to overly alarm China."