You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser.
alternatehistory.com
The challenge, should you accept it, is to form a union of these three crowns with a POD no earlier than 1460.
Bonus points if this blob somehow becomes a dominant world power sometime after 1500. And if you want an extra-harder challenge, try getting Portugal into the mix too!