Answer
The religious upheaval during Mary's regency in Scotland stemmed from the country's transition from Catholicism to Protestantism, fueled by the Scottish Reformation. Tensions escalated as Mary, a devout Catholic, clashed with Protestant lords who sought to establish their faith and consolidate power. This conflict, coupled with Mary's marriage to the Protestant Lord Darnley and her subsequent abdication, plunged Scotland into a period of political and religious turmoil.