Question: Which intergovernmental military alliance signed in 1949 are Denmark and the Netherlands both members of? 
Context: The Collective Security Treaty Organization (CSTO; Russian: Организация Договора о Коллективной Безопасности , "Organizacija Dogovora o Kollektivnoj Bezopasnosti", ODKB) is an intergovernmental military alliance that was signed on 15 May 1992.  In 1992, six post-Soviet states belonging to the Commonwealth of Independent States—Russia, Armenia, Kazakhstan, Kyrgyzstan, Tajikistan, and Uzbekistan—signed the Collective Security Treaty (also referred to as the "Tashkent Pact" or "Tashkent Treaty").  Three other post-Soviet states—Azerbaijan, Belarus, and Georgia—signed the next year and the treaty took effect in 1994.  Five years later, six of the nine—all but Azerbaijan, Georgia, and Uzbekistan—agreed to renew the treaty for five more years, and in 2002 those six agreed to create the Collective Security Treaty Organization as a military alliance.  Uzbekistan rejoined the CSTO in 2006 but withdrew in 2012. The Islamic Military Alliance (IMA), officially the Islamic Military Alliance to Fight Terrorism (IMAFT) , alternative translation Islamic Military Counter Terrorism Coalition, is an intergovernmental counter-terrorist alliance of countries in the Muslim world, united around military intervention against ISIL and other counter-terrorist activities.  Its creation was first announced by Mohammad bin Salman Al Saud, Saudi Arabia's Minister of Defense, on 15 December 2015.  The alliance was to have a joint operations center in Riyadh, Saudi Arabia. The North Atlantic Treaty Organization (NATO ; French: "Organisation du Traité de l'Atlantique Nord" ; "OTAN "), also called the North Atlantic Alliance, is an intergovernmental military alliance between several North American and European states based on the North Atlantic Treaty that was signed on 4 April 1949. NATO is the North Atlantic Treaty Organization, an intergovernmental military alliance. Denmark–Netherlands relations are foreign relations between Denmark and the Netherlands.  Denmark has an embassy in The Hague and the Netherlands has an embassy in Copenhagen.  Both countries are full members of NATO and the European Union.  Princess Beatrix is a Dame of the Order of the Elephant since 29 October 1975.  On 31 January 1998, King Willem-Alexander of the Netherlands also received the Order of the Elephant. The United States European Command (EUCOM) is one of nine Unified Combatant Commands of the United States military, headquartered in Stuttgart, Germany.  Its area of focus covers 21000000 sqmi and 51 countries and territories, including Europe, Russia, Greenland, and Israel.  The Commander of the United States military EUCOM simultaneously serves as the Supreme Allied Commander, Europe (SACEUR) within NATO—an intergovernmental military alliance.  During the Gulf War and Operation Northern Watch, EUCOM controlled the forces flying from Incirlik Air Base. The Treaty of Copenhagen or Treaty of 1670 was a treaty of commerce and alliance signed on July 11, 1670, between King Christian V of Denmark and of Norway and King Charles II of England and of Scots.  It was written in Latin.  It was expanded the next day on July 12, 1670, with the Third Article concerning contraband amended and clarified by a declaration in French signed at Copenhagen on July 4, 1780.  The terms of the treaty were later reaffirmed by the Treaty of Kiel, following the defeat of Denmark-Norway during the Napoleonic Wars. The North Atlantic Treaty Organization or NATO ( ; French: "Organisation du traité de l'Atlantique Nord (OTAN)" ), also called the (North) Atlantic Alliance, is an intergovernmental military alliance based on the North Atlantic Treaty which was signed on 4 April 1949. The Anglo-Soviet Agreement was a formal military alliance signed by the United Kingdom and the Soviet Union against Germany on July 12, 1941; shortly after the German invasion of the latter.  Both powers pledged to assist each other and not make separate peace with Germany. The Austro–Serbian Alliance of 1881 was a secret political alliance signed on 28 June 1881 between the Austro-Hungarian Empire and the Principality of Serbia.  It resulted in the effective association of Serbia with Austria-Hungary and the coming Triple Alliance.  The Balkans had been divided into spheres of influence, where Austria took the western part (including Serbia) and Russia took the eastern part (including Bulgaria).  The treaty came after the railway convention of 6 April 1881 for the construction of the Belgrade–Niš section of the Vienna–Constantinople railway, and the trade treaty of 6 May 1881 which made Austria-Hungary virtually the sole market for agricultural products from Serbia and thereby dominant.
Answer: NATO