Peacekeeping
With the passage of resolution 73 (1949) by the Security Council in August 1949, UNTSO was given the task of fulfilling four Armistice Agreements between the state of Israel and the Arab states which had participated in the war. Thus, UNTSO's operations were spread through five states in the region—Israel, Egypt, Jordan, Lebanon and the Syrian Arab Republic.

Cold War peacekeeping: In the wake of independence in India and Pakistan in August 1947 and the subsequent bloodshed that followed the Security Council adopted resolution 39 (1948) in January 1948 in order to create the United Nations Commission for India and Pakistan (UNCIP), with the purpose of mediating the dispute between India and Pakistan over Kashmir and the fighting related to it. This operation was non-interventionist in nature and was additionally tasked with supervision of a ceasefire signed by Pakistan and India in the state of Jammu and Kashmir. With the passage of the Karachi agreement in July 1949, UNCIP would supervise a ceasefire line that would be mutually overseen by UN unarmed military observers and local commanders from each side in the dispute. UNCIP's mission in the region continues to this day, now under the operational title of the United Nations Military Observer Group in India and Pakistan (UNMOGIP).
Since then, sixty-nine peacekeeping operations have been authorised and have deployed to various countries all over the world. The great majority of these operations have begun in the post-Cold War world. Between 1988 and 1998 thirty-five UN operations had been established and deployed. This signified a substantial increase when compared with the periods between 1948 and 1978; which saw the creation and deployment of only thirteen UN Peacekeeping operations and zero between 1978 and 1988.
Armed intervention first came in the form of UN involvement in the wake of the Suez Crisis in 1956. United Nations Emergency Force (UNEF-1), which existed from November 1956 to June 1967 was essentially the first ever United Nations peacekeeping force. It was given the mandate of ensuring the cessation of hostilities between Egypt, the United Kingdom, France, and Israel in addition to overseeing the withdrawal of French, Israeli and British troops from Egyptian territory. Upon completion of said withdrawal, UNEF would serve as a buffer force between Egyptian and Israeli forces in order to supervise conditions of the ceasefire and contribute to a lasting peace.
Shortly thereafter, the United Nations Operation in the Congo (ONUC), was deployed in 1960. This operation involved upwards of 20,000 military personnel at its peak, and resulted in the death of 250 UN personnel, including then Secretary-General Dag Hammarskjold. ONUC was meant to ensure the withdrawal of Belgian forces in the Congo, who had reinserted themselves after Congolese independence in the wake of a revolt carried out by the Force Publique (FP), in order to protect Belgian citizens and economic interests. ONUC was also tasked with establishing and maintaining law and order (helping to end the FP revolt and ethnic violence) as well as provide technical assistance and training to Congolese security forces. An additional function was added to ONUC's mission, in which the force was tasked with maintaining the territorial integrity and political independence of the Congo—resulting from the secession of the mineral-rich provinces of Katanga and South Kasai. The UN forces there, somewhat controversially, more or less became an arm of the Congolese government at the time and helped to forcefully end the secession of both provinces.

Throughout the 1960s and 1970s the UN created multiple short-term missions all over the world including the Mission of the Representative of the Secretary-General in the Dominican Republic (DOMREP), the UN Security Force in West New Guinea (UNSF), the UN Yemen Observation Mission (UNYOM), in conjunction with more long-term operations such as the UN Peacekeeping Force in Cyprus (UNFICYP), the UN Emergency Force II (UNEF II), the UN Disengagement Observer Force (UNDOF) and the UN Interim Force in Lebanon (UNIFIL).

Since 1991: Experiences of peacekeeping during the Yugoslav Wars, especially failures such as the Srebrenica Massacre, led, in part, to the United Nations Peacebuilding Commission, which works to implement stable peace through some of the same civic functions that peacekeepers also work on, such as elections. The Commission currently works with six countries, all in Africa. In 2013 the U.N. Security Council unanimously passed Resolution 2122, which among other things calls for stronger measures regarding women's participation in conflict and post-conflict processes such as peace talks, gender expertise in peacekeeping missions, improved information about the impact of armed conflict on women, and more direct briefing to the Council on progress in these areas. Also in 2013, the Committee on the Elimination of Discrimination against Women (CEDAW), a UN women's rights committee, said in a general recommendation that states that have ratified the UN Women's Rights Convention are obliged to uphold women's rights before, during, and after conflict when they are directly involved in fighting, and/or are providing peacekeeping troops or donor assistance for conflict prevention, humanitarian aid or post-conflict reconstruction.
The Committee also stated that ratifying states should exercise due diligence in ensuring that non-state actors, such as armed groups and private security contractors, be held accountable for crimes against women.
One of the findings of Page Fortna about where peacekeepers go is that "peacekeeping is a matter of supply and demand" From the supply side, she observes that there is unlikely a Peacekeeping mission in civil wars on countries close to one of the members of the Security Council. From the demand side, there is diverse evidence that peacekeeping missions are deployed in the countries who need it the most, this is where the risk of a recurring war is high.

Composition of peacekeeping forces: 

Nations that participate in peacekeeping missions: The United Nations Charter stipulates that to assist in maintaining peace and security around the world, all member states of the UN should make available to the Security Council necessary armed forces and facilities. Since 1948, about 130 nations have contributed military and civilian police personnel to peace operations. While detailed records of all personnel who have served in peacekeeping missions since 1948 are not available, it is estimated that up to one million soldiers, police officers and civilians have served under the UN flag on its 71 missions. As of September 2021, 122 countries were contributing a total of around 76,000 military observers, police, and troops.
Despite the large number of contributors, the greatest burden continues to be borne by a core group of developing countries. The ten largest troop contributing countries (including police and military experts) to UN peacekeeping operations as of October 2021 were Bangladesh (6447), Nepal (5536), India (5481), Rwanda (5263), Ethiopia (4856), Pakistan (3949), Egypt (2818), Indonesia (2818), Ghana (2296), and China (2248). More than 14,000 civilian personnel serve in peacekeeping operations as legal or medical experts, educators, communication technology professionals, or administrators as of October 2021.
As of September 30, 2021, 4147 people from over 100 countries have been killed while serving on peacekeeping missions. India has the highest number of peacekeeper casualties with 174, followed by Bangladesh (159), Pakistan (159), Nigeria (157), Ghana (145), Ethiopia (138), Canada (123), France (115) and the United Kingdom (106). Since 1948, 56 peacekeepers have been killed each year on average, but recent decades have seen this number almost double, with 110 deaths per year since 2001. 30% of the fatalities in the first 55 years of UN peacekeeping occurred between 1993 and 1995.
There is a strong North-South divide in peacekeeping in that developing nations from the Global South provide the overwhelming majority of peacekeepers. Thomas G. Weiss and Giovanna Kuele argue that this is due to three factors: regional interests, prestige, and financial benefits. African countries are the largest contributors of peacekeepers, but the continent also has the highest number of peacekeeping missions, and most African peacekeepers serve on African missions. As an example, almost all 4800 Ethiopian peacekeepers are deployed in its neighboring countries of Sudan and South Sudan. Being a contributor to peacekeeping missions also provides some international prestige for developing countries, and can bolster countries' claims to be a great power as in the case of Brazil and India. Lastly, providing peacekeepers can have financial benefits for poorer countries. The monthly rate of reimbursement per peacekeeper includes $1,028 for pay and allowances; $303 supplementary pay for specialists; $68 for personal clothing, gear and equipment; and $5 for personal weaponry. Both the direct payments and the training and equipment provided by UN peacekeeping missions can be financially attractive to individual soldiers and developing nations. About 4.5% of the troops and civilian police deployed in UN peacekeeping missions come from the European Union and less than one percent from the United States.
With regard to mission leadership, Force Commanders often come from large troop contributors, while the Special Representatives of the Secretary General often come from developed countries.