A single 60-word sentence passed three days after 9/11 has been used to justify US military operations in at least 22 countries.

Signed into law weeks after the attacks, the PATRIOT Act granted federal agencies sweeping powers to monitor communications, access records, and conduct surveillance—sparking ongoing debates over privacy, civil liberties, and national security.

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.

In the wake of 9/11, the US declared a Global War on Terror—initiating military operations in Afghanistan and Iraq, expanding surveillance, and forming international coalitions to combat terrorism and disrupt extremist networks worldwide.

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.

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.

The collective defense clause of the NATO constitution has only been invoked one time: after the 9/11 terrorist attacks against the United States. This video explores the immediate actions NATO took to respond to the attacks to support the United States. These firsthand clips from 2001 give a sense of the magnitude of the moment and the difficult decisions facing NATO leaders at the time.

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.

The article was invoked the day after the attacks and launched a series of NATO campaigns to fight global terrorism. This page includes excerpts from a speech by then-NATO Secretary General Jens Stoltenberg about the attacks and the organization’s response.

The Insurrection Act of 1807 allows the president to send federal troops into American states during unrest or rebellion, even without a governor's consent. The modern use of the law grants broad discretion and limited congressional or judicial oversight.

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.

In a Gallup poll taken days after the attack, an extraordinary 97% of Americans approved Congress declaring war on Japan—reflecting overwhelming national unity in the wake of the strike.

As part of its post-9/11 strategy, the US employed enhanced interrogation, extraordinary rendition, and secret CIA black sites—practices widely criticized as torture and violations of international law and human rights.

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.

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.

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.

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.

In the weeks following 9/11, 79% of US adults reported displaying the American flag, and a year later, 62% said they "often felt patriotic" due to the attacks.

Under current US policy, the president alone can order the use of atomic weapons at any time without requiring prior approval from Congress—a power rooted in the president's role as commander in chief.

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 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 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.

When Lincoln blockaded Confederate ports at the start of the Civil War without congressional authorization, the Supreme Court upheld his actions, ruling that a president does not initiate war by responding to an attack and need not wait for Congress when the nation is already under threat.

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.

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.

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.

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.

After the attack, Hawaii was placed under sweeping military rule—curfews, censorship, warrantless arrests, ID papers, and mass detentions transformed everyday life. More than 2,000 people were arrested within 48 hours of the attack, and the islands remained under martial law for nearly three years.

President Bill Clinton first called for the National Moment of Remembrance in 1999, and Congress made it law in 2000. The time was chosen because most Americans are in the middle of holiday activities.

In a 6-3 decision, the court held that the International Emergency Economic Powers Act—a 1977 law granting the president authority to regulate commerce during national emergencies—does not authorise the president to unilaterally impose tariffs, a power the Constitution reserves to Congress.

This National Geographic episode reconstructs the events of 9/11—highlighting the Pentagon attack, Flight 93 hijacking, South Tower collapse, and rescue efforts—offering a detailed, chronological account of how the day unfolded.

American Airlines Flight 77 crashed into the Pentagon's west side, destroying a section of the building and killing all 59 on board, along with 125 military and civilian personnel, making it the deadliest attack on the US military headquarters.

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.

In August 1964, Washington claimed that North Vietnam launched two attacks on US destroyers in the Gulf of Tonkin. The second, used to justify escalating the US war effort, was later revealed to most likely have been a radar mistake.

Abraham Lincoln suspended habeas corpus, expanded the army without congressional approval, and issued the Emancipation Proclamation—despite likely lacking authority to unilaterally alter national slave law. His actions set precedents for expanded presidential power in wartime.

In a 2020 podcast from the National Constitution Center, historians and political scientists examine how Congress navigated past national crises—particularly the Civil War—and what those moments reveal about governing today.

Delivered to a joint session of Congress on Dec. 8, 1941, President Franklin D. Roosevelt declared Dec. 7 “a date which will live in infamy.” The speech, heard by tens of millions of Americans, helped consolidate national support for entering the war.