On July 1, 2011, the United Nations welcomed its newest member. South Sudan's January referendum on independence and subsequent peaceful separation from Sudan following years of violence marked a high point for U.N. peacekeeping, which had maintained the armistice there since 2005.

Yet, even as this tenuous victory unfolded, the Cȏte d'Ivoire's hellish descent into renewed violence reminded the world of U.N. peacekeeping's inconsistencies, shortcomings, and mounting challenges. Despite the presence of more than 9,000 U.N. peacekeepers, an estimated one million refugees were displaced by escalating violence in the wake of the country's contested November 2010 presidential elections. While U.N. and French forces eventually restored order in April, the peace remains fragile.

Also in Africa, the catastrophe unfolding in Somalia symbolizes some of peacekeeping's most abject failures. Twenty years, two U.N. peacekeeping missions, and one laborious African Union peacekeeping mission have done nothing to restore peace and stability to the Horn of Africa or to alleviate humanitarian crises there. Years of consternation over Somali pirates has shifted to impotent concern over a devastating famine exacerbated by decades of civil war.

What does the current state of affairs tell us about the nature of U.N. peacekeeping? Why, after more than six decades, is its legitimacy still debated regularly in the halls of the U.N. headquarters in New York City?

Undoubtedly, U.N. peacekeeping has restored peace and brought prosperity to millions of inhabitants in conflict zones around the globe.

Yet, expanding expectations for peacekeeping have strained the resources and mechanisms of the United Nations. Operational overstretch, shifting definitions of what peacekeeping should entail, and diminishing contributions (linked to a weakened global economy) are only the most recent obstacles to a function that has long tested the limits of the United Nations.

The Beginnings of United Nations Peacekeeping

In 1945, delegates from 50 nations met in San Francisco to draft a charter for a new international collective security organization determined "to save succeeding generations from the scourge of war." Since 1948, the United Nations (and its now 193 members) has conducted 67 peacekeeping operations from Central America to Southeast Asia.

For the vast majority of devastated populations around the world, the United Nations has become synonymous with peacekeeping. Yet, nowhere in the 111 articles that comprise the United Nations Charter can the word "peacekeeping" be found.

While not consciously chosen, "peacekeeping" operations arose from the UN's driving commitment to avoid the "scourge of war." The all-important justification for this peacekeeping function resides in Chapter VII of the charter, which stipulates that Security Council can authorize military action to safeguard international peace and security and respond to regional instability resulting from aggressive attacks on the sovereignty of member states.

Under Article 43 of this chapter, member states are obligated "to make available to the Security Council, on its call and in accordance with a special agreement or agreements, armed forces, assistance, and facilities … necessary for the purpose of maintaining international peace and security."

The United Nations, like many collective security alliances, was created in response to the last great threat to peace and security, in this case the two world wars. As such, the United Nations was built to respond to interstate conflicts (between two or more recognized states) and to safeguard the sovereignty of its member states. In order to avoid the inertness that plagued its predecessor, the League of Nations, the U.N. was endowed with rather robust enforcement protocols.

Despite its focus on safeguarding international peace and security, the United Nations was not constructed to confront the type of intrastate conflicts (between groups and peoples within a single recognized state) that almost exclusively dominate its peacekeeping agenda today.

Very soon after the United Nations' founding, Cold War tensions complicated decision-making under Article 43. Since any one of the Security Council's Permanent Five (P-5) can exercise veto rights in defense of broader geopolitical agendas, the ability of the U.N. to speak in a unified voice when authorizing military action has often proved difficult—especially as the Cold War animosity between the United States and the Soviet Union crystallized.

Despite these challenges, the United Nations confronted threats to peace and security with military action far more effectively than the League of Nations before it. In so doing, however, it was forced to develop "peacekeeping" within the parameters laid out in Chapter VII's passages on military operations.

First-Generation Peacekeeping

From 1948 until the end of the Cold War in the early 1990s, the U.N. developed first-generation peacekeeping. There are some stark differences between that first iteration and what comprises second-generation U.N. peacekeeping today, but there are also shared characteristics.

Then as now, U.N. peacekeepers had to be invited by the host state and would not deploy until a ceasefire had been established. The invitation protected the sovereignty of member states, a paramount concern for the United Nations, and the ceasefire provided some sign that the belligerents were committed to resolving the conflict.

Yet, first-generation peacekeeping was more passive than it is today. Peacekeepers were deployed to keep the peace, not to restore peace or stop ongoing fighting.

U.N. peacekeeping forces consisted of lightly armed troops deployed to serve in a neutral capacity, physically interposed or inserted between opponents. Since U.N. peacekeepers were primarily a visible deterrent and a reminder of the international community's reciprocal commitment to resolving the conflict, peacekeepers did not need heavy weaponry and intentionally did not project an offensive military capability.

Armed only lightly and with their iconic light blue helmets, U.N. peacekeepers monitored ceasefires and remained in the field only so long as the invitation remained. Once an invitation was rescinded, the United Nations was obligated by its own rules of engagement to withdraw its forces and work to fulfill its mandate by other means.

This approach to peacekeeping was easy to reconcile with the language of the U.N. Charter, thus obviating any need to become fixated on the absence of the term "peacekeeping" in the Charter. Nevertheless, this model was not without serious limitations. Perhaps the best illustration of the challenges associated with first-generation peacekeeping is the initial U.N. Emergency Force (UNEF I) mission that was deployed to the Sinai region of Egypt from 1956 to 1967.

Trial in the Sinai

On October 29, 1956, Israel invaded the Sinai Peninsula of Egypt and quickly advanced westward toward the Suez Canal, which Egypt had nationalized in July to the consternation of Great Britain and France. Under the pretense of protecting the Suez shipping lane from Israeli-Egyptian fighting, British and French paratroopers landed in the canal zone within a few days of the Israeli invasion.

With three foreign forces deployed on its soil, Egypt petitioned the U.N. Security Council for assistance. When it met on October 31, it was stymied by the veto power of both Great Britain and France, so the issue was kicked to the General Assembly for resolution.

Following a ten-day emergency session, General Assembly Resolution 998 (1956) authorized the Security Council to deploy a peacekeeping force to Egypt and called for the immediate withdrawal of British, French, and Israeli forces from Egyptian territory.

U.N. peacekeepers were charged with overseeing these withdrawals and serving as a force physically stationed between Egyptian and Israeli troops in support of the ceasefire agreement. The limited rules of engagement set forth in the mission's mandate authorized the 6,000 peacekeepers to return fire only in self-defense.

For the next decade, UNEF I, deployed on the Egyptian side of the armistice line, patrolled the Sinai frontier and shouldered the burden of preventing a resumption of hostilities with a diminishing number of troops.

Then, in May 1967, the Egyptian government withdrew the invitation to U.N. peacekeepers. Less than three weeks later, the 1967 Six Day War broke out between Egypt and Israel leaving UNEF I with a problematic legacy.

The Sinai example highlights the limitations of the first-generation model of U.N. peacekeeping. Like many of the organization's military operations, the U.N. Security Council was susceptible to the intransigence of its five permanent members.

Even when stalemates could be avoided, the limited nature of first-generation peacekeeping meant there was often a split verdict on its utility. On one hand, UNEF I maintained the peace between two hostile neighboring states for 10 years. On the other hand, it did very little to resolve the underlying cause of the conflict as demonstrated by the outbreak of war once U.N. peacekeepers were out of the picture.

Second-Generation Peacekeeping

Second-generation peacekeeping was born on the fly and out of a necessity to address the far more complex nature of the ethnic and communal violence that increasingly confronted the United Nations at the end of the Cold War. It moved peacekeeping beyond the passive interposition role into something far more involved and multidimensional.

The early 1990s ushered in a short-lived optimism about U.N. peacekeeping. Tensions among the P-5seemed to dissipate and many looked forward to a new era of peacekeeping operations purged of the partisanship generated by Cold War adversaries.

The grim flip side was that many of the smaller conflicts that the Cold War superpowers had held at bay were now free to explode unchecked. In the absence of Soviet or American patronage, many developing states around the globe began to fracture and spiral into chaos fueled by resurgent nationalism, political instability, and contested natural resources.

The United Nations confronted an alarming proliferation of bloody and primal intrastate conflicts throughout much of the Global South. Its first-generation model of peacekeeping now appeared inadequate and ill-designed for these new types of clashes.

The United Nations was forced to expand its understanding of what peacekeeping entailed to include long-term conflict resolution. Peacekeeping quickly evolved from a limited role of symbolic deterrence primarily charged with monitoring an existing ceasefire to an active one that involved in-depth conflict resolution and peace enforcement. U.N. peacekeeping crept ever closer to peace implementation and enforcement.

Peacekeeping remained predicated on preventing the resumption of hostilities between warring parties, but beginning in the 1990s, its approach to resolving the underlying conflict also became more robust. United Nations peacekeeping missions were increasingly charged with laying the foundation for a self-sustaining peace: implementing political solutions to the conflict, shoring up transitional governments, providing economic assistance for post-conflict states, and shouldering the responsibility for humanitarian assistance during the transition period.

One of the lessons taken away from UNEF I was the need for peacekeepers to be more involved in resolving the underlying conflict. Adhering strictly to an interposition role was insufficient because it did little to create conditions for a lasting peace in the absence of international actors.