On the western front, the main objective of the British invasion of 1759 was Fort Niagara. Under the command of General John Prideaux, 5,500 British and American soldiers left from Albany, accompanied by 600 Iroquois warriors led by Sir William Johnson, reached the proximity of the French fort at the beginning of July. The garrison, under the command of Commander Pierre Pouchot, was barely 500 men.
In spite of the overwhelming superiority of the Anglo-American forces, Pouchot declined the offer to surrender, and on July 9 the siege began. The Anglo-Americans had to dig trenches to protect the siege cannon, because Niagara was not typical of the forts of western North America. Since 1755, the French had been building bastions and glacis like those used in the fortifications erected in Europe by Maréchal Vauban. Prideaux thought it was better to shell the fort with mortar fire while conducting siege operations in the European fashion with parallel sapping trenches. On July 17 the heavy British cannon, installed at last, were put into action. The French responded immediately. In the British camp, in a single day, July 20, two senior ranking officers, a lieutenant-colonel and a colonel, were mortally wounded. But the worst was yet to come: that very evening, General Prideaux was killed accidentally by one of his own mortars. Refusing to give up, Sir William Johnson took command of the army. Four days later, at La Belle Famille, a few kilometres to the south of the fort, he crushed the reinforcing troops from Illinois and Ohio, which consisted of approximately 800 soldiers and militiamen, supported by 600 Amerindians. The next day, giving up all hope of further assistance, Pouchot surrendered. 
French communications to the West were cut off from that moment on.