An Anglo-Spanish dynastic union in 1560

What changes if the English and Spanish empires unite around 1560?

The union would overwhelm nearby rivals at sea and radically alter Scotland, the Dutch revolt, the Reformation, and the later religious character of Atlantic colonization.

The scenario requires Mary I to live longer and produce an heir with Philip II, creating a dynastic union rather than a later British imperial merger. Combined English and Spanish fleets would make French support for Scotland much harder and remove English backing from Dutch independence. England would become a major Catholic power instead of one of Protestant Europe's anchors. That change reaches across the Atlantic because the political and religious forces behind later English colonization would develop differently. The panel ultimately cautions that the consequences are so large that precise answers become speculative fiction.