Since World War II, formal declarations of war and peace treaties have become increasingly rare, replaced by cease-fires, authorizations of force, and "special military operations."

Congress has formally declared war 11 times across five conflicts, the last in 1942

The five declared wars were the War of 1812, the Mexican-American War, the Spanish-American War, World War I, and World War II. Every major American military conflict since Korea, Vietnam, Iraq, and Afghanistan has been fought without a formal declaration.

Presidents have often used military force without formal declarations of war

Although the Constitution grants Congress the power to declare war, American presidents have repeatedly ordered military action without formal declarations. These precedents have expanded executive authority in national security beyond what the framers likely envisioned.

A formal declaration of war automatically triggers hundreds of statutes granting the president sweeping domestic authority

Beyond authorizing military force abroad, a formal declaration activates a wide range of domestic powers, including authority over enemy property, trade restrictions, and emergency economic authority. It also waives the 60-day time limits under the War Powers Resolution.

Presidents now rely on executive agreements instead of formal treaties

Formal treaties—requiring two-thirds Senate approval—have become rare in American foreign policy. Modern presidents increasingly use executive agreements, which don't need congressional consent, allowing faster diplomacy but reducing legislative oversight and transparency.

Truman's decision to enter the Korean War without congressional authorization marked a major shift in presidential war powers

Rather than seeking a declaration of war, Truman sent troops to Korea under his own authority, citing the UN Charter and his role as commander in chief. The decision set a precedent that subsequent presidents have relied on ever since.

A legal scholar argues that the existing war powers framework may collapse in the event of a major power conflict

The legal tests presidents have used to avoid seeking congressional authorization were designed for weaker adversaries. This piece argues that those tests fail against similarly armed competitors, where even limited strikes risk significant escalation, potentially triggering a constitutional crisis over who has the authority to respond.

The first test of America's war powers came just a decade after the Constitution was ratified

During the undeclared Quasi-War with France in 1800, the Supreme Court ruled in Bas v. Tingy that Congress had authorized a valid "imperfect war" through statutes alone, without a formal declaration, establishing that there is a legal spectrum between peace and declared war.

At the 1787 Constitutional Convention, Madison changed the draft language from Congress's power to "make" war to "declare" war

The change was deliberate: "make" war seemed to leave the president unable to defend the country against sudden attack, while "declare" preserved that defensive authority. The distinction between starting a war and responding to one has been debated ever since.

The US never formally declared war in Vietnam

Instead of formally declaring war, Congress passed the Gulf of Tonkin Resolution in 1964, granting President Johnson broad authority to use military force. The resolution became the legal basis for escalating US involvement without an official declaration of war.

The War Powers Act may have ironically given presidents more discretion to engage in hostilities, not less

In this wide-ranging podcast on Congress's power to declare war, scholar Gary Schmitt argues that the War Powers Act, ironically, gave presidents a legal framework for initiating hostilities, creating a 60-day window for unilateral action that hadn't existed before.

Relationships between countries have become more peaceful since the rules-based order was established

Our World in Data monitors bilateral relationships on a spectrum from open rivalry to "positive peace"—deep cooperation and mutual protection. In 1945, no countries had highly cooperative security relationships. Today, nearly a fifth do.

War-making authority is divided between Congress and the president in the Constitution

Article I grants Congress the power to declare war and fund the military, while Article II makes the president commander in chief. However, the Constitution does not clearly delineate where one authority ends and the other begins, creating a tension that has never been fully resolved.

In the 1930s, Congress nearly passed a constitutional amendment requiring a national vote before declaring war

The Ludlow Amendment, proposed amid rising isolationism after World War I, would have required a national referendum before Congress could declare war, except in cases of direct attack. It was defeated 209 to 188 in 1938 after Roosevelt lobbied against it.

The global nuclear arms regime has slowly eroded over the past few decades

Both Russia and the United States have withdrawn from key Cold War-era arms-control pacts. Russia's 2022 invasion of Ukraine marked a turning point, as it suspended its participation in inspections and data-sharing agreements.

The Supreme Court has never definitively settled federal war powers

Despite more than two centuries of conflict over war powers, the Supreme Court has consistently avoided defining the precise boundary between congressional and executive authority, leaving that boundary to be contested by the political branches.

The threat of nuclear annihilation reshaped global diplomacy

The first use of atomic weapons introduced the possibility of a war with no survivors. This article examines how nuclear fear shaped Cold War diplomacy and continues to influence international relations today.

Wartime conferences exposed cracks in the US–Soviet alliance

At the Tehran, Yalta and Potsdam Conferences, Allied leaders coordinated WWII strategy—but deep disagreements over postwar Europe foreshadowed the Cold War. The USSR’s push for influence in Eastern Europe clashed with US and British calls for self-determination.

Presidents from both parties have resisted the authority of the War Powers Act

Presidents from both parties have treated the War Powers Resolution as voluntary, framing compliance as seeking "support" rather than "permission." Courts have declined to rule on the law's constitutionality each time a related case was brought before them.

Because the Korean War ended with an armistice rather than a peace treaty, North and South Korea are technically still at war.

Free speech has often been restricted in wartime, potentially unconstitutionally

From the Sedition Act of 1798 to the prosecution of anti-war activists during World War I, the US government repeatedly curtailed speech and dissent during wartime—actions widely criticized and, in some cases, later deemed unconstitutional.

Ceasefires rarely produce a total cessation of violence.

The treaty that ended the First World War laid the groundwork for the Second.

The power and influence of the American presidency have expanded significantly over time—far beyond what the founders envisioned.

History shows what’s wrong with the idea that war is ‘normal’ in the Middle East

An old trope claims that war is ‘normal’, innate, and inevitable in the Middle East. However, the history of the region reveals complex and civilized systems of coexistence. Empires found economic and political strength in fostering diversity;...

During the Cold War and into the 21st century, US and Soviet/Russian leaders repeatedly agreed to arms control treaties, though strained tensions have led to the expiration of agreements in recent years.

The War Powers Act of 1973 was passed over Nixon's veto to limit the president's ability to wage war unilaterally

Passed in the aftermath of the Vietnam War, the War Powers Resolution requires the president to notify Congress within 48 hours of deploying forces and to end military operations within 60 days without congressional approval. Nixon vetoed the bill, arguing it was unconstitutional, but Congress overrode his veto.

The “Phoney War” was an eight‑month build-up to war

From September 1939 to May 1940, following their war declaration on Germany, Britain and France entered a phase of military inaction—even as civil defence measures, naval blockades, and rationing intensified at home. Skirmishes were limited, but the decisive fighting didn't begin until Germany invaded Norway and France in April–May 1940, abruptly ending the uneasy stalemate.

Proponents argue that abandoning the rules-based order risks a return to the chaos that led to 2 world wars

Brookings scholar Robert Kagan warns that if China and Russia gain regional dominance, the world could return to the unstable conditions of the late 19th century—the same chaos that led to two devastating world wars.

During the Cold War, the rules-based order was largely limited to the West

The Soviet Union and its allies operated outside the Bretton Woods institutions, meaning the postwar liberal order functioned as a regional rather than a truly global system. This changed with the USSR's collapse in 1991.

The Concert of Europe was an earlier attempt to manage great power relations through shared rules

After the Napoleonic wars, European powers established a system of regular consultation to manage conflicts and maintain the balance of power. It offered relative stability for nearly a century before deteriorating.

In his 1859 annual message to Congress, President Buchanan articulated a narrow view of presidential military authority

Buchanan argued that the president lacked constitutional authority to launch offensive military action without congressional approval, a view that reflected the prevailing interpretation of executive war powers throughout much of the nineteenth century.

The world rapidly decolonized after World War II, with roughly a hundred new countries emerging between 1945 and 1989.

Decolonization isn't complete, as nearly 2 million people were living in UN-designated non-self-governing territories as of 2023.

Four Cold War hawks warn: Nuclear weapons still threaten the world

Despite the Cold War's end, the US and Russia still hold 95% of the world's nuclear weapons—many on hair-trigger alert. In this 2010 documentary, top former officials urge urgent action to reduce and eliminate the threat.

The 2001 Authorization for Use of Military Force has been used by five administrations to justify military operations in at least 22 countries.

The treaty's Article 5 requires mutual defense, but not necessarily military action.

The Cold War (1947-1991) prompted the birth of NATO and the Soviet Warsaw Pact

The geopolitical rivalry between the United States and Soviet Union was considered “cold" because the two countries never directly engaged in military combat during the time period. This page from the Kennedy Presidential Library outlines the causes and major events of the early Cold War.

Much of the Global South responded to the Russia-Ukraine war by pursuing a strategy of 'active nonalignment'

Boston University scholar Jorge Heine suggests that countries across Africa, Asia, and Latin America are avoiding taking sides between Washington and Beijing—viewing the rules-based order as increasingly unresponsive to the needs of developing nations and considering the West's framing of the war irrelevant to its own interests.

NATO was formed in 1949 to deter Soviet expansion, prevent European militarism, and encourage political integration.

Congress has unsuccessfully voted on war powers resolutions over Trump's military operations in Venezuela and Iran

After Trump ordered unilateral military operations in both Venezuela and Iran without congressional authorization, lawmakers from both parties introduced war powers resolutions to block further action. Each effort failed, with Republican majorities largely supporting the president.

NATO has only invoked its mutual defense clause once, in the days after the 9/11 attacks.

The failures of the interwar period made the case for a new international system

After World War I, countries devalued their currencies, raised tariffs to block imports, and seized territory unchecked, with the international community unable to organize effectively to stop them. The result was a global depression and, eventually, another world war.

Members decide to what extent they respond to an attack on an ally

The NATO constitution is intentionally vague about what exactly is required from its members. Explore the historical debates and learn more about common misconceptions about NATO’s common defense clause.

Youngstown Sheet & Tube Co. v. Sawyer established the framework courts use to evaluate presidential war powers

When Truman seized US steel mills during the Korean War, the Supreme Court ruled that he had overstepped his authority. Justice Jackson's concurring opinion held that presidential power is strongest when Congress authorizes action, uncertain when Congress is silent, and weakest when Congress explicitly refuses authorization.

Nixon argued that the War Powers Resolution unconstitutionally restricted his authority

In his veto message, Nixon argued that the resolution would dangerously curtail the president's ability to respond to international crises and that only a constitutional amendment could properly define the limits of executive war powers. Congress disagreed and overrode the veto.

The Barbary Wars were an early test of whether a president could wage war without a formal declaration from Congress

Jefferson sent naval forces against North African pirates without a congressional declaration of war, acting under his own authority. Years later, Madison took the opposite approach and formally sought congressional authorization.

Defining the use of 'Third World' in geopolitics

The term "Third World" is mostly out of use today for its limiting connotations, but in light of a reordering of geopolitical alliances amid the Ukraine war, historians are reevaluating the term's usefulness. Read the history of the term starting from the 1950s, and learn what several experts claim about its contemporary efficacy.

The 1956 Suez crisis was one of the earliest tests of the rules-based order

When Britain, France, and Israel secretly invaded Egypt, the Eisenhower administration supported UN resolutions condemning the invasion and called for a ceasefire—publicly criticizing its closest allies to uphold the principle that force should not be used to resolve international disputes.

Explore every War Powers Resolution report submitted to Congress since 1973

This NYU School of Law project catalogs all unclassified 48-hour reports submitted by presidents since the War Powers Resolution was enacted, with search options by president, location, and claimed legal authority.

Russia's invasion of Ukraine accelerated fractures in the rules-based international order

This piece examines how the Ukraine conflict intensified underlying divisions in the global order—between Western democracies and the Global South, and between rule-of-law norms and great-power politics.

How Stalin, Roosevelt, and Churchill shaped the postwar world

The Yalta Conference was a pivotal 1945 meeting between Allied leaders that helped shape the postwar global order and laid the groundwork for the founding of the United Nations.