In 1594, the Nine Years' War in Ireland had begun, when Ulster lords Hugh O'Neill and Red Hugh O'Donnell rose up against English rule with fitful Spanish support, mirroring the English support of the Dutch rebellion. While English forces were containing the rebels in Ireland at great cost in men, general suffering and finance, the Spanish attempted two further armadas, in 1596 and 1597: the first was shattered in a storm off northern Spain, and the second was frustrated by adverse weather as it approached the English coast. King Philip II died in 1598, and his successor Philip III continued the war but was less determined. At the end of 1601, a final armada was sent north, this time a limited expedition intended to land troops in southern Ireland to assist the rebels. The Spanish entered the town of Kinsale with 3,000 troops and were immediately besieged by the English. In time, their Irish allies arrived to surround the besieging force but the lack of communication with the rebels led to an English victory at the Battle of Kinsale. Rather than attempt to hold Kinsale as a base to harry English shipping, the Spanish accepted terms of surrender and returned home, while the Irish rebels hung on, surrendering in 1603, just after Elizabeth died. The new king of England, James I, was the Protestant son and successor to the Catholic Mary, Queen of Scots, whose execution had been a proximate cause of the war. James regarded himself as the peacemaker of Europe, and the ultimate aim of his idealistic foreign policy was the reunion of Christendom. Therefore, when James came to the English throne, his first order of business was to negotiate a peace with Philip III of Spain.
Question: whose execution had been a proximate cause of the war?
Answer: Catholic Mary, Queen of Scots