King James' Oath of Allegiance Published in English
Shortly after the 1605 Gunpowder Plot imploded, Parliament passed a new law that required Catholics in England to take an Oath of Allegiance to King James and, simultaneously, to publicly deny the Pope's international political power--specifically the pontiff's "right" to depose Kings. Pope Paul V immediately condemned the English law, and sent letters to James demanding satisfaction. Instead of giving the task to a cleric or functionary, James decided to write a reply--an "apology" (an explanation) himself. This tract was printed in February 1608 as Triplici Nodo Triplex Cuneus, anonymously, and in Latin.
On April 8, 1609 (date on the title page) the book was revised and re-issued in English giving King James credit for the book publicly.
"An Apologie for the Oath of Allegiance, first set foorth without a name : And now acknowledged by the Author, the Right High and Mightie Prince James. Together with a Premonition of his Maiesties, to all most Mightie Monarches, Kings, free Princes and States of Christendome. Imprinted at London by Robert Barker, Printer to the Kings most Excellent Majestie April 8, ANNO 1609."
Also new in the 1609 edition was James' Premonition -- an appeal to other Protestant princes and kings. He refers to the Gunpowder Plot as the "Powder Treason."
It is odd that Shakespeare did not deal with Gunpowder Plot allusively -- unless he did. Garry Wills' 1995 Witches and Jesuits [Shakespeare's Macbeth] argues that Macbeth allegorizes the Gunpowder plot. This is still controversial. Many Shakespeare scholars do not accept Wills' thesis. I don't.
If you're curious, here's a review of Wills' book and theory:
And here's the wiki page on the Plot: