They were originally divided into different clans (although they were still under Mandalores leadership).Each member would fight to bring honour to their clan.
The Mandalorians were founded by a race called the Taung, however in later years became a collection of multiple species (although prodominantly human) including Wookiee and Twi'lek ( and possily Trandoshan).They were also mixed gender.
When ever a Mandalore died another Mandalorian would rise to replace them, they could be of any species/breed and of any gender.
Despite being of multiple species,they were united by a common belief. Eventually stopped worshipping their god and began worshipping war itself.around 4000 years prior to the events of A New Hope the Mandalorians reached their hight of power, and in 3995 B.A.N.H ( possibly
with Sith interfeirance) declared war on the Republic.Brushing aside the Republic's navy they conquered many worlds in their search for power (although they were eventually stopped 34 years later with the death of Mandalore).
Other engagements the Mandalorians participated in were The Great Sith War and the new Sith wars,(The Mandalorians being lead by a Mandalor who was also a Sith) again against the Republic.Though these are only a small number of potentially thousands of campaigns the Mandalorians fought in.
In later years the Mandalorians became a mercinary army for hire under a succession of leaders, the final two being; Jaster Mereel and Jango Fett.
The Mandalorians were eventually extinguished as a fighting force during an ambush involving a jedi called Count Dooku and their enemies the Death Watch another Mandalorian clan who the True Mandalorians led by Jaster Meerel were at war with. At the battle of Galidraan 44 years B.A.N.H., in which most of the captured ended up imprisoned in a maximum security prison on an asteroid called Oovo IV.
However some Mandalorians are known to have escaped either being captured or from the prison itself, these include Jango Fett, Montross and Chopp'aa Notimo.
Although defeated, the Mandalorians lived on in their enemies the Death Watch who themselves were founded by a Mandalorian splinter group led by Tor Vizsla and a larger group of Mandalorians that turned to a more peaceful existence (though never fully rid themselves of their armour or way of fighting and of which Boba Fett became Mandalore).