The North Atlantic Treaty Organization is a military alliance between several European and North American countries that was founded in 1949. Its 29 Member States assure each other military assistance in case of an outside attack. This provision, known as Article 5 of the NATO treaty, has only been invoked once, following the September 11 attacks. Other challenges NATO dealt with counter-piracy, peace-keeping operations and humanitarian missions. Recently, cooperation and mutual training support have become more important again, especially in light of a possible confrontation with Russia.