The visit by Japan’s prime minister, Shinzo Abe, to the United States next week is important on several levels. He will be the first Japanese leader to address a joint meeting of Congress. He and President Obama are expected to announce progress on a key issue, increased defense cooperation, and possibly on a second, trade. They will also discuss a third challenge, China’s growing influence in Asia.

The context is also important: This year is the 70th anniversary of Japan’s defeat in World War II, and to some extent the visit is intended as a celebration of the country’s remarkable postwar resurrection and its robust alliance with an old enemy, which has become a foundation of regional stability.

But the success of the visit also depends on whether and how honestly Mr. Abe confronts Japan’s wartime history, including its decision to wage war, its brutal occupation of China and Korea, its atrocities and its enslavement of thousands of women forced to work as sex slaves or “comfort women” in wartime brothels.

By now, that history should have been settled. That it is not settled is largely the fault of Mr. Abe and his right-wing political allies who keep questioning history and even trying to rewrite it, stoking regional tensions. Mr. Abe may have more to say on all this on Aug. 15, the actual date of the surrender. But his remarks to Congress will send an important signal.

Mr. Abe’s nationalist views and pressure from competing political forces have affected his judgment on these delicate issues. He has publicly expressed remorse for the war and said he will honor Japan’s past apologies for its aggression, including the sex slavery. Yet he has added vague qualifiers to his comments, creating suspicions that he doesn’t take the apologies seriously and will try to water them down. ...