In the international arena, cooperation is good and conflict is bad. Unfortunately, conflict is also dramatic , and leaders who engage in it tend to get attention while instances of cooperation often pass unnoticed. A president who fights a war makes the history books; wars avoided are rarely commented on. So it's worth taking time to note that despite -- or, rather, because of -- the lack of drama during this week's presidential trip to Russia, something hugely important happened: A deal on steep bilateral reductions in nuclear weapons has made the world a much safer place. The lack of drama is, itself, a noteworthy turn of events. Ever since Vladimir Putin's leadership and high oil prices allowed Russia to regain the state capacity it largely lost in the 1990s, the United States and Russia have had some persistent differences of perspective. Most notably, the U.S. wants to see the former Soviet republics treated like real independent states. Russia, by contrast, looks at its so-...