The original purpose of NATO (the North Atlantic Treaty Organization) was to provide collective security to its member nations. Articles III and V of the NATO charter both explicitly state this purpose, with article V characterizing an "armed attack against" one of its member states as an "attack against them all." In this sense, NATO has served the region quite well, and, it could be argued, maintained peace in Europe after World War II. In recent years (i.e., after the Cold War and the collapse of the Soviet Union), NATO's purpose has expanded. It has added more member nations, and multiple NATO countries send forces under NATO commanders to serve in Afghanistan, which multi-national forces invaded in 2001. Additionally, many observers are questioning whether NATO is capable of restraining the strategic threat many see in Vladimir Putin's Russia, especially in light of its inactivity in the face of Russia's seizure of the Crimean peninsula. President Donald Trump has attempted to pressure European nations into spending more on NATO, pointing out that the United States shoulders a disproportionate burden of funding. In short, while NATO has its share of problems, it is difficult to see an alternative to this alliance system that, most would agree, helped preserve peace during the Cold War.