Armenia and Azerbaijan have agreed to exchange prisoners of war and work toward signing a peace treaty in what the European Union is hailing as a major step toward peace in the long-troubled region. The two countries said in a joint statement Thursday that they “share the view that there is a historical chance to achieve a long-awaited peace.” Azerbaijan waged a lightning military campaign in September in the separatist region of Nagorno-Karabakh. The offensive ended three decades of rule there by ethnic Armenians and resulted in the vast majority of the 120,000 residents fleeing the region, which is internationally recognized as part of Azerbaijan.