Analysis of information sources in references of the Wikipedia article "Barbarian" in English language version.
The list of barbarians who have 'come' and 'seen' as mercenaries, before imposing themselves as conquerors, is a long one.
Of all the barbarian peoples in the Han period, the Hsien-pi were probably most interested in trade. [...] [T]he Chinese frontier generals often hired them as mercenaries [...], which [...] was a result of the Later Han policy of 'using barbaians to attack barbarians.'
[...] by the fifth century the Roman army had effectively been transformed into an army of barbarian mercenaries.
The Vikings, for instance, made for particularly convenient soldiers of fortune [...]. [...] Other 'barbarian' groups, including the Alans, Cumans, and Pechenegs, also found their services to be in demand, particularly from the Byzantine and Turkish empires (Vasary 2005). Perhaps the most famous, and certainly the most reliable early mercenaries were the Byzantine Varangian Guard.
This model of Byzantine 'state-owned slave-soldiers' and mercenaries from the Barbarian North of the 'Seventh Climate' was subsequently imitated by the Umayyad and Abbasid Caliphs who also had their own 'Ṣaqālibah' troops and Varangian-like bodyguards.
The list of barbarians who have 'come' and 'seen' as mercenaries, before imposing themselves as conquerors, is a long one. [...] The Turkish bodyguard of the 'Abbasid Caliphs in the ninth century of the Christian Era prepared the way for the Turkish buccaneers who carved up the Caliphate into its eleventh-century successor-states.
It now seems that the use of military mercenaries became widespread, with central Mexican groups brought in by the Maya and Maya-Gulf Coast groups penetrating the Central Mexican Highlands.
[...] in the spring of 1595 the Turks began to strike back against Christian armies [...] and a major European war was detonated. [...] There were advantages for the cossacks no matter which side was winning. Throughout the war there was a steady stream of envoys of foreign rulers coming to the sich to bid for cossack support [...] mercenaries such as the cossacks were needed.
[I]n 1816 the Gurkha mercenary tradition began. Although the soldiers known as Gurkhas would fight in the British service and, later, in the Indian service as well, Nepalese rulers also hired out soldiers to other foreign powers.
"The status of being a foreigner, as the Greeks understood the term does not permit any easy definition. Primarily it signified such peoples as the Persians and Egyptians, whose languages were unintelligible to the Greeks, but it could also be used of Greeks who spoke in a different dialect and with a different accent ... Prejudice toward Greeks on the part of Greeks was not limited to those who lived on the fringes of the Greek world. The Boeotians, inhabitants of central Greece, whose credentials were impeccable, were routinely mocked for their stupidity and gluttony. Ethnicity is a fluid concept even at the best of times. When it suited their purposes, the Greeks also divided themselves into Ionians and Dorians. The distinction was emphasized at the time of the Peloponnesian War, when the Ionian Athenians fought against the Dorian Spartans. The Spartan general Brasidas even taxed the Athenians with cowardice on account of their Ionian lineage. In other periods of history the Ionian-Dorian divide carried much less weight."
"The status of being a foreigner, as the Greeks understood the term does not permit any easy definition. Primarily it signified such peoples as the Persians and Egyptians, whose languages were unintelligible to the Greeks, but it could also be used of Greeks who spoke in a different dialect and with a different accent ... Prejudice toward Greeks on the part of Greeks was not limited to those who lived on the fringes of the Greek world. The Boeotians, inhabitants of central Greece, whose credentials were impeccable, were routinely mocked for their stupidity and gluttony. Ethnicity is a fluid concept even at the best of times. When it suited their purposes, the Greeks also divided themselves into Ionians and Dorians. The distinction was emphasized at the time of the Peloponnesian War, when the Ionian Athenians fought against the Dorian Spartans. The Spartan general Brasidas even taxed the Athenians with cowardice on account of their Ionian lineage. In other periods of history the Ionian-Dorian divide carried much less weight."
