England's break with Rome unfolded inside a wider Atlantic competition already shaped by the papal division of Iberian claims under the Treaty of Tordesillas. English mariners had challenged Spanish and Portuguese overseas monopolies even while England remained Catholic. After the Reformation, Spain could no longer appeal to a religious authority recognized by the English crown to restrain that activity. England therefore had stronger reason to invest in a navy capable of protecting an island realm, controlling its maritime approaches, and supporting overseas ambitions.
Chapter · 9:48-11:41
The Reformation turns sea power into an English necessity
The Treaty of Tordesillas, religious division, and overseas rivalry explain why England had to treat the surrounding seas as its first line of security.