After the fall of the Berlin Wall in Germany in 1989 , the organization conducted its first military interventions in Bosnia from 1992 to 1995 and later Yugoslavia in 1999 during the breakup of Yugoslavia . Politically , the organization sought better relations with former Warsaw Pact countries , most of which joined the alliance in 1999 and 2004 . Article 5 of the North Atlantic treaty , requiring member states to come to the aid of any member state subject to an armed attack , was invoked for the first and only time after the September 11 attacks , after which troops were deployed to Afghanistan under the NATO-led ISAF . The organization has operated a range of additional roles since then , including sending trainers to Iraq , assisting in counter-piracy operations and in 2011 enforcing a no-fly zone over Libya in accordance with UN Security Council Resolution 1973 . The less potent Article 4 , which merely invokes consultation among NATO members , has been invoked five times following incidents in the Iraq War , Syrian Civil War , and annexation of Crimea
September 11 attacks
September 11 attacks
NATO