CAMBRIDGE - Will military power become less important in the coming decades? It is true that the number of large-scale inter-state wars continues to decline, and fighting is unlikely among advanced democracies and on many issues. But, as Barack Obama said in accepting the Nobel Peace Prize in 2009, we must begin by acknowledging the hard truth that we will not eradicate violent conflict in our lifetimes. There will be times when nations - acting individually or in concert - will find the use of force not only necessary but morally justified.