Before taking office, President-elect Donald Trump described the American-led North Atlantic Treaty Organization, or NATO, as "obsolete." NATO formed in 1949 to protect Europe from potential military aggression from the Soviet Union. It's motto: An attack on one nation is an attack on all. When the Soviet Union dissolved and Cold War ended NATO stayed in tact and its membership grew to include 28 nations. Now, three years after Russia's annexation of the Crimean Peninsula in Ukraine and an uptick in aggression by Russian President Vladimir Putin, the Obama administration has sent thousands of American troops to Eastern Europe to reinforce NATO. NewsHour Weekend Special Correspondent Christopher Livesay reports from Germany and Poland.