Military
Main article: United States Armed Forces
The president is the commander-in-chief of the United States Armed Forces and appoints its leaders, the secretary of defense and the Joint Chiefs of Staff. The Department of Defense administers five of the six service branches, which are made up of the Army, Marine Corps, Navy, Air Force, and Space Force. The Coast Guard, also a branch of the armed forces, is normally administered by the Department of Homeland Security in peacetime and can be transferred to the Department of the Navy in wartime.[278] In 2019, all six branches of the U.S. Armed Forces reported 1.4 million personnel on active duty.[279] The Reserves and National Guard brought the total number of troops to 2.3 million.[279] The Department of Defense also employed about 700,000 civilians, not including contractors.[280]

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The nuclear-powered aircraft carrier USS George Washington (CVN 73)
Military service in the United States is voluntary, although conscription may occur in wartime through the Selective Service System.[281] From 1940 until 1973, conscription was mandatory even during peacetime.[282] Today, American forces can be rapidly deployed by the Air Force's large fleet of transport aircraft, the Navy's 11 active aircraft carriers, and Marine expeditionary units at sea with the Navy, and Army's XVIII Airborne Corps and 75th Ranger Regiment deployed by Air Force transport aircraft. The Air Force can strike targets across the globe through its fleet of strategic bombers, maintains the air defense across the United States, and provides close air support to Army and Marine Corps ground forces.[283][284][285] The Space Force operates the Global Positioning System, operates the Eastern and Western Ranges for all space launches, and operates the United States' Space Surveillance and Missile Warning networks.[286][287][288] The military operates about 800 bases and facilities abroad,[289] and maintains deployments greater than 100 active duty personnel in 25 foreign countries.[290]

The United States spent $649 billion on its military in 2019, 36% of global military spending.[291] At 4.7% of GDP, the rate was the second-highest among the top 15 military spenders, after Saudi Arabia.[291] Defense spending plays a major role in science and technology investment, with roughly half of U.S. federal research and development funded by the Department of Defense.[292] Defense's share of the overall U.S. economy has generally declined in recent decades, from early Cold War peaks of 14.2% of GDP in 1953 and 69.5% of federal spending in 1954 to 4.7% of GDP and 18.8% of federal spending in 2011.[293] In total number of personnel, the United States has the third-largest combined armed forces in the world, behind the Chinese People's Liberation Army and Indian Armed Forces.[294]

The United States is one of the five recognized nuclear weapons states, and one of nine countries to possess nuclear weapons. It has the world's second-largest stockpile of nuclear weapons, after that of Russia. The United States also owns more than 40% of the world's 14,000 nuclear weapons.[295]

Law enforcement and crime
Main articles: Law enforcement in the United States and Crime in the United States
See also: Law of the United States, Human rights in the United States § Justice system, Incarceration in the United States, Sheriffs in the United States, Police brutality in the United States, and Capital punishment in the United States
A New York City Police Department cruiser vehicle
The New York City Police Department is the nation's largest municipal law enforcement agency.
Law enforcement in the United States is primarily the responsibility of local police departments and sheriff's offices, with state police providing broader services. Federal agencies such as the Federal Bureau of Investigation (FBI) and the U.S. Marshals Service have specialized duties, including protecting civil rights, national security and enforcing U.S. federal courts' rulings and federal laws.[296] According to the Bureau of Justice Statistics, and Charles H. Ramsey, former Philadelphia, Pennsylvania police chief, appearing on Meet the Press, there are about 18,000 U.S. police agencies in the United States. That number includes city police departments, county sheriff's offices, state police/highway patrol and federal law enforcement agencies.[297] State courts conduct most criminal trials while federal courts handle certain designated crimes as well as certain appeals from the state criminal courts.

A cross-sectional analysis of the World Health Organization Mortality Database from 2010 showed that United States homicide rates "were 7.0 times higher than in other high-income countries, driven by a gun homicide rate that was 25.2 times higher."[298] In 2016, the U.S. murder rate was 5.4 per 100,000.[299]

Chart depicting a steep increase in the number of incarcerated Americans from the 1980s to the 2000s
Total incarceration in the United States by year (1920–2014)
The United States has the highest documented incarceration rate and largest prison population in the world.[300] The Department of Justice said that the imprisonment rate for all prisoners sentenced to more than a year in state or federal facilities in 2019 stood at 419 per 100,000 residents which was at its lowest point since 1995 and that the total prison population for the same year stood at 1,430,800 which represented an 11% decrease in the population size from a decade earlier.[301] Other sources such as the Prison Policy Initiative had put the aggregate number of prisoners in 2020 at 2.3 million.[302] According to the Federal Bureau of Prisons, the majority of inmates held in federal prisons are convicted of drug offenses.[303] Efforts to reduce the prison population include government policies and grassroots initiatives that promote decarceration — recent examples include laws at the federal and state level such as the Fair Sentencing Act, First Step Act, Maryland's Justice Reinvestment Act and California's Money Bail Reform Act. About 9% of prisoners are held in privatized prisons,[302] a practice beginning in the 1980s and a subject of contention.[304] On January 26, 2021, the Biden Administration signed an executive order that halted the renewal of federal government contracts with private prisons,[305][306] but it did not apply to detention centers that held undocumented immigrants.[307]

Although most nations have abolished capital punishment,[308] it is sanctioned in the United States for certain federal and military crimes, and at the state level in 28 states, though three states have moratoriums on carrying out the penalty imposed by their governors.[309][310][311] In 2019, the country had the sixth-highest number of executions in the world, following China, Iran, Saudi Arabia, Iraq, and Egypt.[312] No executions took place from 1967 to 1977, owing in part to the 1972 U.S. Supreme Court ruling in Furman v. Georgia that struck down the previous practice. Since the decision, however, there have been more than 1,500 executions, although 186 of those convicted and sentenced since Furman have been exonerated, as tabulated by the Death Penalty Information Center.[313] In recent years, the number of executions and presence of capital punishment statute on whole has trended down nationally, with several states recently abolishing the penalty.[311][314]