"Soldiers" may be referred to by titles, names, nicknames, or acronyms that reflect an individual's military occupation specialty arm, service, or branch of military employment, their type of unit, or operational employment or technical use such as: trooper, tanker (a member of tank crew), commando, dragoon, infantryman, guardsman, artilleryman, paratrooper, grenadier, ranger, sniper, engineer, sapper, craftsman, signaller, medic, rifleman, or gunner, among other terms.

Some of these designations or their etymological origins have existed in the English language for centuries, while others are relatively recent, reflecting changes in technology, increased division of labor, or other factors.

[3] One example of a nickname for a soldier in a specific occupation is the term "red caps" to refer to military policemen personnel in the British Army because of the colour of their headgear.

came into common use during World War II and after, but prior to and during World War I especially, American soldiers were called "Doughboys," while British infantry troops were often referred to as "Tommies" (short for the archetypal soldier "Tommy Atkins") and French infantry were called "Poilus" ("hairy ones").

Until the American Civil War, Black soldiers fought in integrated and sometimes separate units, but at other times were not allowed to serve, largely due to fears about the possible effects of such service on the institution of legal slavery.

After the war, Black soldiers continued to serve, but in segregated units, often subjected to physical and verbal racist abuse.

In 1948, President Harry S. Truman issued an executive order for the end of segregation in the United States Armed Forces.

In the United States, males aged 18-25 are required to register with the Selective Service System, which has responsibility for overseeing the draft.

In a study of 18th century soldiers' written records about their time in service, historian Ilya Berkovich suggests "three primary 'levers' of motivation ... 'coercive', 'remunerative', and 'normative' incentives.

"[8] Berkovich argues that historians' assumptions that fear of coercive force kept unwilling conscripts in check and controlled rates of desertion have been overstated and that any pay or other remuneration for service as provided then would have been an insufficient incentive.

The study found that "soldiers join the Army for family, institutional, and occupational reasons, and many value the opportunity to become a military professional.

Such service, depending on the army's need for staffing or the individual's fitness and eligibility, may involve fulfillment of a contractual obligation.