REUTERS/Ints Kalnins NATO shifted its focus to other issues outside of Europe in the years after the Cold War. But the alliance has in recent years refocused on deterring Russia, which has modernized its military and is more active around the world. The alliance is now challenged by both conventional threats and irregular tactics, Secretary General Jens Stoltenberg said this month. New security challenges in Europe require new responses and more vigilance from NATO, according to Secretary General Jens Stoltenberg, who said this month that the lines between conflict and competition are becoming less distinct. NATO was formed by European and North American countries in 1949 to provide collective defense against Soviet aggression and to help rebuild and integrate Europe.