Introduction
How is the Military in United States and how does it work to maintain Sucity and fight terrorism? In terms of Military and security forces, we have the United States Armed Forces (aka US Military): US Army (USA), US Navy (USN; includes US Marine Corps or USMC), US Air Force (USAF), US Space Force (USSF); US Coast Guard (USCG); National Guard (Army National Guard and Air National Guard) (2024).
In United States, the US is a member of NATO and was one of the original 12 countries to sign the North Atlantic Treaty (also known as the Washington Treaty) in 1949

the US military's primary missions are to deter potential enemies, provide for the defense of provide for the defense of the US, the Territories, Commonwealths and possessions, and any areas occupied by the US, and to protect US national interests; it has worldwide responsibilities; the separate services operate jointly under 11 regional- or functionally-based joint service "combatant" commands: Africa Command; Central Command, Cyber Command, European Command, Indo-Pacific Command, Northern Command, Southern Command, Space Command, Special Operations Command, Strategic Command, and Transportation Command

Congress officially created the US military in September 1789; the US Army was established in June 1775 as the Continental Army; after the declaration of independence in July 1776, the Continental Army and the militia in the service of Congress became known collectively as the Army of the United States; when Congress ordered the Continental Army to disband in 1784, it retained a small number of personnel that would form the nucleus of the 1st American Regiment for national service formed later that year; both the US Navy and the US Marines were also established in 1775, but the Navy fell into disuse after the Revolutionary War, and was reestablished by Congress in 1794; the first US military unit devoted exclusively to aviation began operations in 1913 as part of the US Army; the Army Air Corps (AAC) was the US military service dedicated to aerial warfare between 1926 and 1941; the AAC became the US Army Air Forces in 1941 and remained as a combat arm of the Army until the establishment of the US Air Force in 1947 (2024)
Security and military information of United States
Military and security service personnel strengths approximately 1.31 million active-duty personnel (446,000 Army; 328,000 Navy; 317,000 Air Force; 9,000 Space Force; 167,000 Marine Corps; 40,000 Coast Guard); 330,000 Army National Guard; 105,000 Air National Guard (2024)
Military equipment inventories and acquisitions the US military's inventory is comprised almost entirely of domestically produced weapons systems (some assembled with foreign components) along with a smaller mix of imported equipment from a variety of Western countries such as Germany and the UK; the US defense industry is capable of designing, developing, maintaining, and producing the full spectrum of weapons systems; the US is the world's leading arms exporter (2024)
Military service age and obligation 18 years of age (17 years of age with parental consent) for voluntary service for men and women; no conscription (currently inactive, but males aged 18-25 must register with Selective Service in case conscription is reinstated in the future); maximum enlistment age 34 (Army), 42 (Air Force/Space Force), 39 (Navy), 28 (Marines), 31 (Coast Guard); 8-year service obligation, including 2-5 years active duty (Army), 2 years active duty (Navy), 4 years active duty (Air Force, Coast Guard, Marines, Space Force) (2023). note 1: the US military has been all-volunteer since 1973, but an act of Congress can reinstate the draft in case of a national emergency

note 2:
all military occupations and positions open to women; in 2021, women comprised over 17% of the total US active duty military personnel; a small number of American women were involved in combat during the Revolutionary (1775-1783), Mexican (1846-1848), and Civil (1861-1865) Wars, but they had to disguise themselves as men and enlist under aliases; the first official US military organization for women was the US Army Nurse Corps, established in 1901; during World War I, the US Navy and Marine Corps allowed women to enlist; nearly 350,000 women served in the US military during World War II; the 1991 Gulf War was the first war where women served with men in integrated units within a war zone; in 2015, women were allowed to serve in direct combat roles

note 3: non-citizens living permanently and legally in the US may join as enlisted personnel; must have permission to work in the US, a high school diploma, and speak, read, and write English fluently; minimum age of 17 with parental consent or 18 without; maximum age 29-39, depending on the service; under the US Nationality Act, honorable service in the military may qualify individuals to obtain expedited citizenship; under the Compact of Free Association, citizens of the Federated States of Micronesia, the Republic of Palau, and the Republic of the Marshall Islands may volunteer; under the Jay Treaty, signed in 1794 between Great Britain and the US, and corresponding legislation, Native Americans/First Nations born in Canada are entitled to freely enter the US and join the US military
Military deployments the US has more than 200,000 air, ground, and naval personnel deployed overseas on a permanent or a long-term rotational (typically 3-9 months) basis; key areas of deployment include approximately 5,000 in Africa, approximately 100,000 in Europe, approximately 10-15,000 in Southwest Asia, and more than 80,000 in East Asia (2024).
Military expenditures
Military Expenditures 2024 3.4% of GDP (2024 est.)
Military Expenditures 2023 3.2% of GDP (2023)
Military Expenditures 2022 3.3% of GDP (2022)
Military Expenditures 2021 3.5% of GDP (2021)
Military Expenditures 2020 3.6% of GDP (2020)
Terrorism
In United States, the different Terrorist group(s) inlcude: Hizballah; Islamic Revolutionary Guard Corps (IRGC)/Qods Force; Islamic State of Iraq and ash-Sham (ISIS); al-Qa'ida; Lashkar-e Tayyiba (LeT)
All Important Facts about United States

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United States is found in North America