The Invasion of Hanover took place in 1757 during the Seven Years' War when a French army under Louis Charles César Le Tellier, duc d'Estrées advanced into the Electorate of Hanover and neighbouring German states following the Battle of Hastenbeck. French forces overran most of Hanover forcing the Hanoverian Army of Observation, intended to defend the Electorate, to Stade on the North Sea coast. At the Convention of Klosterzeven the Duke of Cumberland agreed to disband his army and acknowledge the French occupation of the Electorate.