Complex sentence: Pitt is best known as the wartime political leader of Britain in the Seven Years War, especially for his single-minded devotion to victory over France, a victory which ultimately solidified Britain's dominance over world affairs.
Split into simpler sentences: Pitt is best known as the wartime political leader of Britain in the Seven Years War, especially for his single-minded devotion to victory over France. A victory which ultimately solidified Britain's dominance over world affairs.