For young people growing up in the U.S. today, war is the norm. News of drone strikes, bomb explosions, and military deployments in countries around the world have become mundane.

Political observers have argued that this type of perpetual warfare is technically illegal, citing the U.S. Constitution and federal law. But for nearly 20 years, Democratic and Republican presidential administrations alike have gotten away with killing foreign citizens by relying on an ambiguous, now-controversial resolution that was passed by Congress three days after the 9/11 attacks.

The War Powers Resolution grants Congress authority to declare war

According to the Constitution, declaring war is the responsibility of Congress. After a rebellion against a king with broad, unchecked powers, the Constitution’s framers were wary of handing over such a grave responsibility to one person alone; instead, they dispersed that responsibility across hundreds of congressional representatives to debate the merits of a potential military conflict and then vote on it.

Alexander Hamilton, a leading proponent for a strong central government, explained the president's limited war-making authority in the Federalist Papers: Whereas the king of Britain had the authority to declare war, he wrote, the new Constitution would give the president of the United States the responsibility of carrying out the war as commander in chief of the military, and “nothing more.”

In reality, however, deliberative war-making has not been the norm since World War II, which was the last time Congress made a declaration of war. The old model — Congress issues a formal, committed, and absolute declaration following a deliberative process and formal vote — didn’t quite fit the United States’ new Cold War military strategy of engaging in proxy military conflicts against Soviet-backed movements in countries throughout the so-called “Third World.”

Beginning largely with the Korean War, U.S. presidents started to deploy the military around the world without congressional authorization to stave off what they feared was growing Soviet influence. During this period, and most consequently for the future of U.S. politics, Democratic and Republican administrations launched devastating bombings and military campaigns in Vietnam, Cambodia, and Laos without any meaningful congressional input.

In response to presidential usurpation of war-making powers, Congress passed the War Powers Resolution in 1973. This new law put several limits on the president’s authority to make war unilaterally, including a provision stating that after a president deploys military forces into conflict, they must notify Congress within 48 hours. Congress then has 60-90 days to declare war or authorize that deployment; if it chooses to do neither, the president is obligated to withdraw the military.

A bill passed after 9/11 gave presidents new cover for military interventions

President Nixon tried unsuccessfully to veto the War Powers Resolution, and subsequent presidents have plainly ignored it. In 1981, Ronald Reagan sent troops to El Salvador, and in 1991, Bill Clinton bombed Kosovo — both without seeking proper authorization from Congress.

But today’s endless wars truly began three days after 9/11. On September 14, 2001, both houses of Congress passed the Authorization for Use of Military Force of 2001 (AUMF), which became law four days later, giving George W. Bush an unambiguous mandate to retaliate against groups and individuals responsible for the attacks on September 11.

Soon after receiving that authorization, President Bush invaded Afghanistan to target al-Qaeda, the group behind the attacks, and the Taliban, the group “harboring” al-Qaeda in Afghanistan. He then quickly expanded the scope of the conflict and the authorization, using it to initiate the global War on Terror, launching military campaigns everywhere, including Georgia, the Philippines, Kenya and Yemen. At the same time, the Bush administration used the authorization to establish a system of indefinite detention at Guantanamo Bay and committed a host of human rights abuses around the world.