While the meeting between U.S. President Donald Trump and Russian President Vladimir Putin in Alaska underscored the Arctic’s decisive importance, there was another signal coming from just offshore: Russian and Chinese naval forces conducting a joint exercise near the Aleutians. In the north Indo-Pacific, a geostrategic game is unfolding, one in which control over sea lanes, resources and influence will shape the 21st century. And Washington has been slow to catch up. Despite Alaska’s undeniable role in the Indo-Pacific, providing a launch pad for force projection and missile defense, for three decades America has let its Pacific Arctic flank erode....