Compare and contrast the ways that seventeenth-century
absolute monarchs and twentieth-century dictators gained and
maintained their power.

Important differences - Unlike the other two, Charles I was not associated with any political Party, and had not "risen through the ranks" to become Leader. As a King, he achieved his position by heredity, and since no-one can choose their parents, this was used to justify the doctrine of "Divine Right" - God dedcides that a child shall be born into a Royal succession, and it is blasphemy to make any attempt to change this. Similarly, it was therefore the "will of God" that he should be succeeded by one of his children - the eldest son, in the English and Scottish tradition. In England, there was also the unusual situation that, as well as being Head of State, the King was also Head of a particular religious organization - the "Church of England" - which meant that he could not be expected to recognise any other form of Christianity. It was his enforcement of this which aroused resistance by such men as Cromwell, who was against any enofrced religon, and for "liberty of conscience". (This was why Cromwell subsequently also opposed Parliament when it attempted to enforce Presbyterianism,) There is perhaps case for seeing a similarity in Stalin, since "Marxist/Leninist Communism" was in fact a "religion", even though a godless one. There are virtually no comparisons with Hitler.