Can't comment on the others, but I can talk about the Norman conquest.

William, duke of Normandy, was born in 1028. He was an illegitimate son, therefore he had the nickname of "the bastard". Anyways, William's claim to the English throne was based on the claim that in 1051 the English king Edward "the Confessor" had promised him the throne,. Edward was childless and thus succession was kinda up in the air.

However, when Edward was on his deathbed he gave the throne to Harold Godwine, the head of one of the most, if not the most powerful noble family in England ( even more powerful than the king). It was also said by William that Harold had sworn on a holy relic to support William's kingship. This usurping outraged William who invaded while Harold was distracted by Harald Hardrada and his brother Tostig.

Sources: 1066: The Year of the Conquest William the Conqueror by David Bates