How could England get conquered as many times as possible, with a POD that doesn't prevent the 1066 invasions?
Failed invasions don't count, but successful invasions with only short-term effects do. Conquests of most of England, but not all of it, do count. As does the emplacement of puppet kings if they eventually lead to full conquest.
The butterfly effect can be interpreted conservatively if necessary. For example people outside of Europe who were born after 1066 could still be born.
Here's a list of the successful invasions of England before 1066:
- Caesar's second invasion (no strict conquest, but established dominance)
- Claudius' conquest of Britain
- Angle and Saxon migrations
- Viking conquest of Danelaw
- Sweyn Forkbeard's conquest of England
- Cnut the Great's conquest of England
And in 1066, there were three pretenders against Harold Godwinsson:
- William the Bastard of Normandy
- Harald Hardrada of Norway
- Sweyn II Estridsson of Denmark
So how many more times could England be conquered from 1066?
I'd suggest that Harald actually kills Harold instead of the other way around. Maybe Harald marches to and takes London. William ends up killing King Harald Hardrada of England, not Harold Godwinsson.
William is then crowned King. But the Danish invasion/Anglo-Saxon rebellions of 1069 still happen, perhaps with greater Danish support due to more Norwegian success earlier. Danes conquer England from William only a few years afterward.
But it's likely this conquest would be short-lived since the already small Danish forced would be cut down, the Anglo-Saxons were rebellious, and the Normans would be antagonized.
So another revolt probably happens, deposing Sweyn II. One of his sons, several of whom either fought in the 1069 invasion or invaded England later, invades and probably conquers England because of possible Norwegian support.
What could happen from here? Would Norman claimants after William is defeated come back? Would they be successful?
Would any continental powers be interested in England? How would they justify an invasion and could they succeed?