On December 31, 1603, Jacques-Auguste de Thou, president of the Parlement of Paris and royal librarian to Henry IV of France, wrote a congratulatory letter to King James VI of Scotland who had recently ascended the English throne. De Thou's purpose, apart from celebrating the close joining of the French, Scottish, and English royal houses in James's lineage, was to present the monarch with a copy of his recently published book. This was the first volume of the Historia sui temporis, a work which was soon to be regarded as one of the authoritative histories of the tumultuous events in France and Europe in the second half of the sixteenth century. Henry IV, said de Thou, had urged him to send the British king a copy, and he had generously said that it should be inscribed to James. De Thou's letter specifically asked James, who was now cultivating new friendships and taking on new duties, to promote “the concord of the Church with common consent,” rather than limiting himself to establishing peace within his own borders.

Religious reconciliation, particularly in France, had long been one of de Thou's major concerns. Brought up and educated during the French religious wars, he had intended at one time to enter the priesthood of the Roman Catholic Church, but he had become, instead, a lawyer active in public life and had served as a counsellor to both Henry III and Henry IV.