John Churchill (1650-1722), the son of Sir Winston Churchill (1620-1688), was born in Ashe, Devon, England in 1650. Churchill's father, a Royalist loyal to King Charles I and II and known as the Cavalier Colonel, was made a Member of Parliament after the English Civil War. His son John made great advances in the military, starting with a commission in the foot guards in 1667. After his marriage to Sarah Jennings (1660-1744), Churchill rose rapidly through the ranks. When James II (formerly the Duke of York) became king in 1685, Churchill was made a lieutenant general and peer of the realm. Churchill displayed political acumen, switching his allegiances to William of Orange in 1688 when the Catholic James II was forced from power in favor of the Protestant Dutch duke. For his loyalties to William III, Churchill was made earl of Marlborough.

Marlborough temporarily lost royal favor in the 1690s. In the early 18th century when King Louis XIV of France began maneuvering for control of Spain's throne and empire, William III appointed Marlborough to take control of England's military campaigning against France. After William III died and his daugther Queen Anne took the throne, Marlborough crossed the Channel to take control of English and Dutch forces and fight against the French. His efforts in these campaigns led Queen Anne to make him a duke.

Marlborough created the Grand Alliance, a coalition of small and large European powers opposing France's ambitions. His victories against France, including at the battles of Blenheim, Ramillies, and Oudenaarde, secured him a military reputation unrivaled until Napoleon Bonaparte's of the following century.

Marlborough's wife Sarah was a close friend and confidant of Queen Anne's; they had an ally in Sidney, earl of Godolphin (1645-1712), who served as lord treasurer and, in effect, prime minister, though the role did not truly exist until 1721. By 1710, political fracturing over the war and between the Tories and Whigs led Queen Anne to dismiss Godolphin from his post. In 1711 the queen dismissed Malborough from all his public appointments. He and his wife lived abroad for the rest of Queen Anne's reign, and though he was restored to favor under King George I and the duke and duchess returned to England, Marlborough never again held a political or military appointment.

Sarah Jennings entered the Duke of York's household in 1673, becoming friends with his daughter Anne. John Churchill was at court at the same time, and she was secretly married to him in 1677-1678, as his parents opposed the match, which did not provide any financial gain to the Churchill family. Princess and later Queen Anne relied heavily on the Duchess of Marlborough's counsel and companionship until 1705, when Sarah's Whig sympathies irritated Anne's Tory tendencies too much. By 1710, Sarah lost all influence with Queen Anne, and she never again saw the queen.

[Information retrieved from "John Churchill, 1st duke of Marlborough" and "Sarah Jennings, Duchess of Marlborough," britannica.com.]