One down, one to go. No one in the White House or State Department used that phrase in announcing the end of the United States' failed Cuba policy, but it is undoubtedly ringing in the minds of more than a few people in Washington. Ending our hostility toward Cuba not only makes humanitarian sense but also represents a security gain for the United States. Now comes the bigger challenge: rebuilding our relations with Iran.

One of the great benefits of reconciliation with Cuba is that it reduces the possibility of upheaval or instability on the island and opens the prospect of a peaceful transition to democracy. Rapprochement with Iran — which is infinitely more important to the U.S. and the rest of the world — would do the same. If it happens, President Barack Obama will be able to leave office saying he ended both of United States' most self-defeating foreign policies. History would record it as his greatest achievement on the world stage.

This week's breakthrough, wonderful though it is, would have meant far more if it had happened a generation ago. Many of today's young people cannot remember that Cuba was once a major global force able to project power around the world. Today it is poor and weak. Cubans are likely to benefit from better ties to the U.S., and Americans will finally be able to buy Cuban cigars and lie on Cuban beaches. But beyond the two countries directly involved — and perhaps Venezuela, which is Cuba's only real ally — it is not likely to have much impact.