What posted the biggest threat to William from 1066 to 1971

They we're rebellions because The revolt was caused by the king's refusal (in his absence - he had been in Normandy since 1073) to sanction the marriage between Emma (daughter of William Fitzosbern, 1st Earl of Hereford and Adelissa de Tosny) and Ralph de Guader, Earl of East Anglia in 1075. They married without his permission.

There was rebellions