I'm sure that many here are familiar both with the Kipling's poem "Danegeld" and with the tax raised to pay off Norse raiders who harried Dark Ages England.
Kipling's poem contains the line:
"And that is called paying the Dane-geld; But we've proved it again and again, That if once you have paid him the Dane-geld You never get rid of the Dane."
And, of course, this was what happened in this case in point. The Norse kept raiding and eventually just moved right in.
But did it ever work? Was there a case of a barbarian tribe that stayed bought? One that took the money and never came back?
Overall, what's the balance? Is paying off the raiders more likely to cause them to leave, or just stick around and bleed you white?
I think the principles here probably apply to all kinds of extortion. The balance of power is in favour of the extorter, and they'll keep coming back until either you become stronger than them, they decide they're extorting too much and 'killing the goose', they move on to something more attractive or lucrative, or something else intervenes. A lot can happen in history if you just buy yourself some time.
I just had a look at Trevelyan's Shortened History of England and he mentions Danegeld in the reigns of Ethelred and Alfred. Under Etherled the sums were very large, even ruinous, and were a factor in the succession of (the Danish) King Canute. Under Alfred they were smaller, and didn't prevent an effective war with the Danes.
In the broader perspective I'm sure there are examples where aggressors have been successfully bought off. And bear in mind that it's not necessarily worse to be regularly paying people off than to have to raise and maintain an army to fight them off.
England was invaded by Danes, but how do you know they had been paying off Danes specifically, rather than perhaps all Scandianvians being lumped together as 'Danes'? Because archaeological finds have turned up far more English/Anglo-Saxon coins from the Viking Age in Sweden than in any other Nordic country:
| Country | Number |
|---|---|
| Sweden | 37500 |
| Denmark | 5300 |
| Norway | 3300 |
| Finland | 1000 |
| Iceland | 185 |
(Numbers from Fornvännen 78 (1983))