In 1755, when hostilities broke out in North America, George II, king of England and elector of Hanover, negotiated the Treaty of Westminster with Frederick II of Prussia, who guaranteed the neutrality of Hanover. This event hastened the alliance (1756) of France and Austria, sometimes called the "diplomatic revolution." Shortly afterward Frederick II opened hostilities by invading Saxony. In Jan., 1757, war was declared on the aggressor in the name of the Holy Roman Empire. Austria concluded alliances with France and Russia and was joined by Sweden. The main European phase of the war began with the Prussian invasion of Bohemia early in 1757.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.