A professional soldier that hires his or her services is known as a mercenary. An army group of such volunteer soldiers would be mercenaries.
Militia or Volunteers.
Militia
Militia.
militia
Volunteer Military
People's Volunteer Army
if you read, on wikipedia it says Stephen Austin was selected to lead the volunteer army.
Crow
it is a volunteer army
Sam Houston
A person who has to join the army because its his countries law. He or she is not a volunteer.
On formed from people who join the army because they want to, not because they are forced to.
Marquis de Lafayette
The US Army, like the other US Military branches are an all volunteer fighting force, which means you have to volunteer to enlist. With your consent, being able to pass the ASVAB and physical you can then be enlisted into the Army.
Florence Nightengale was a volunteer nurse during the Crimean war. While she was not in the army, she worked in a military hospital in Turkey along with many other volunteer nurses from the UK.
There's no set list, but some of the leading volunteer organizations are the Salvation Army and the American Red Cross. The Salvation Army boasts that they have approximately 3.5 million volunteers.