Is this something that began in the 1800s? 1700s? My understanding of the British from my American education is that the king or queen would have had a huge amount of authority around the time of the American Revolution. So how did this come to change in the interim?
That's largely a quirk of the way the American colonists framed their arguments (as addresses to the King rather than to Parliament). The English and then British monarchy assumed it's constitutional role gradually from the time of the Restoration and Glorious Revolution, which both established Parliamentary supremacy.
Hi, not discouraging others from answering here, but FYI, there are a few posts on this subject here