The "Union of Crowns" refers to the event in 1603 when James VI of Scotland ascended to the English throne as James I, uniting the crowns of Scotland and England. This marked the beginning of a personal union, where both kingdoms were ruled by the same monarch while remaining separate sovereign states. Although the two countries shared a ruler, they maintained distinct laws, parliaments, and systems of governance. The Union of Crowns set the stage for future political developments, ultimately leading to the formal Acts of Union in 1707, which created the Kingdom of Great Britain.