Final answer:
During Empress Elizabeth's reign, the Seven Years' War (1756-1763) occurred, instigated by growing European power rivalries, notably with Frederick the Great's invasion of Saxony. Queen Anne's War focused on the conquest of Acadia.
Step-by-step explanation:
The major war that occurred during the reign of Empress Elizabeth of Russia was the Seven Years' War. This conflict began in Europe in 1756 when Frederick the Great of Prussia invaded Saxony, causing France, Spain, and Russia to join forces with Austria to oppose him, while Great Britain allied itself with Prussia to maintain the balance of power in Europe. A major cause of the Seven Years' War was the growing rivalries between European powers, which led to various nations holding approximately equal military power in an effort to prevent the domination of Europe by any single country.
Queen Anne's War, a different conflict, was significant because it focused on the conquest of Acadia, expanding control over North American territories, as stated in Exercise 6.3.3.