I've tried searching for this one, and I don't understand it. For me, it looks like the only difference is that Union of the Crowns involved Scotland, England and Ireland and it meant to unite those three kingdoms under one king - James VI while Union of England and Scotland was unsuccesful and its purpose was to go beyond the Union of the Crowns in some respects. Can someone please clarify that for me?
The union of the crowns under James VI/I was purely a person union. Two separate countries, England and Scotland, that happened to share the same monarch. England and Scotand still had separate parliaments, legal systems, and armed forces. Kind of like Canada and Australia today, except that the role of the monarch in government was much greater on those days.
The union of 1707 united England and Scotland into one country. The Scottish parliament and armed forces were dissolved and superseded by the new institutions of the Kingdom of Great Britain. (Scotland did retain its own legal system and religious arrangements).