Contrary to popular belief, the Saxon's and tribes made up from Jute's, Angle's, Saxon's, known as the Anglo Saxon's of England, were not barbaric raiders that came from the near by continent, to conquer, rape and pillage, take over from what we are told where the Romano British, they were invited mercenaries.
Picts and Irish
When the Romans withdrew its legions and over seeing governors around 450 AD leaving the British tribes to get on with it, it was not long before the Scottish Picts along with Irish tribes started raiding the north of England crushing the villages and towns the roman empire built, and now abandoned civilized people, they were no match for these (unconquered by Rome) raiders of the north and from across the Irish sea warriors, the Brits were unorganized easy meat and were becoming over run, something had to be done? and quick.
Jutes Angles Saxons
The Jutes, Angles,Saxons, were tribes of people that had been driven to the edge of the north sea by the roman empire and lived on the strips of unconquered land, they had avoided Rome's capture for century's but the life was very tough and resources were almost non existent, so in order for these tribes of people to survive, the populations had to be kept under strict control, every other year a form of straws were drawn to choose fairly, tribal members to be exiled from there increasing populations to maintain their survival and their existence. Those that drew the shortest straw's, were then told to leave and never to return, to fend for themselves where ever they could, this act was backed up by the swearing of an oath, the word oath is Anglo Saxon, translated it means plight! this was and means the plight of the Anglo Saxons, it was never broken by those who gave it, it was a pagan sacred oath, for if they did, the consequence's would have been certain death.
Vortigern greeting Hengist and Horsa
Down in the south east corner of britain was a tribe with a leader called vortigern, this area today is known as kent, having had traded with the people on the other side of the channel sea during the latter falling roman empire days, he knew these tough warrior type people and there fighting skills, very well.
With the raids of the Picts and Irish becoming more and more and reaching ever further down the country he hatched a plan, he sent word to the Jutish king asking for help to fight off the marauding northerners and drive them back, offering land resources and settlement in Britain for fighting mercenaries, the jute king obliged and sent his two princes Hengist and Horsa! when there ships and men landed Vortigern welcomed them with open arms and struck the deal, pledged hes oath with what all he promised.
With these warrior mercenaries and his own men they drove the Picts and Irish back, with ever more similar deals struck with other British tribes and more arrivals of continental mercenaries, eventually the invaders were driven right back across the Irish sea and back to Scotland.
Early Anglo Saxon England
With a form of peace now attained and now living in coexistence with these Jutish mercenaries also other by then, continental tribe's of Saxon and angle's among the British tribes, things were going along nicely until.... Some of the British tribal leaders objected and wanted them all to go back, knowing what the oath meant to these continental warrior tribe's, vortigern tried reasoning but to no avail and fighting broke out, this was to the continental warriors a breaking of there sacred oath, the worse thing to do which meant more than life to them, after all they owed there existence to it for over 400 years! more continental tribes poured in and completely took over killing even Votigern and all the British tribal leaders. the Jutes took over the south east corner, the angles the east coast, and south Saxons along the southern coast, forming what is known today as the Anglo Saxon kingdom.
Oath
The moral of this story is, those that break their oath, suffer the consequences for doing so, in present times most people would not even know what it means let alone swear one, yet it is one of the main foundations of the English culture which formed and created the English nation, and so many others in the western world today.