While the English colonies were growing rapidly along the Atlantic seaboard, French fur traders and explorers were extending long but thinly supported strands of ownership deep into the heart of North America. La Salle's exploration of the Mississippi to its mouth in 1682 gave France a claim to a vast area bordering the American Colonies from the Great Lakes and the Ohio River valley southward to the Gulf of Mexico. It could be only a matter of time before the rivalries between France and England elsewhere in the world would be sharply reflected in a final struggle for the ownership of the North American continent. England's concern over France's threatened control of much more than half the continent began as early as Henry Hudson's last voyage, in the time of Champlain , and the probings for the Northwest Passage by such explorers as Sir Martin Frobisher, John Davis, and William Baffin.

England came to realize that the easiest riches of the New World were to be found in furs rather than in gold. Thus it was quick to follow up its claim to the back-door route to the fur country by founding the Hudson's Bay Company in 1670, on the suggestion of Pierre Esprit de Radisson and Medart Chouart, sieur de Groseilliers

For many years England's domination of Hudson Bay was threatened by the French. In 1686 Pierre Troyes led an amazing overland expedition from Montreal to the shores of the bay, where his followers succeeded in capturing a number of the company forts by surprise. In his party was one of the most daring and brilliant leaders in the history of New France, Pierre le Moyne, sieur d'Iberville. Iberville commanded a series of naval raids into the bay during the next few years and almost succeeded in driving the English from this part of the continent altogether.

A fresh struggle between France and England, known as Queen Anne's War, broke out in 1702 and led to the capture of Port Royal by the English in 1710. The Treaty of Utrecht, which reestablished peace in 1713, required France to surrender the Hudson Bay Territory, Newfoundland, and Acadia. France was permitted to keep Cape Breton Island as well as her inland colonies.

As an immediate result of this setback, France founded the powerful Fortress of Louisbourg on Cape Breton Island. It was to serve as a year-round military and naval base for France's remaining North American empire and also to protect the entrance to the St. Lawrence River. Louisbourg was developed into the most heavily fortified bastion in North America during the next 25 years.

In 1745 an army of New Englanders led by Sir William Pepperell mounted an expedition of 90 vessels and 4,000 men against Louisbourg. The fortress had become a hornet's nest of raiders who preyed on the merchant ships of the American Colonies. Within three months the New Englanders succeeded in forcing Louisbourg to surrender. The fortress was returned to France, however, by the Treaty of Aix-la Chapelle signed in 1748.

To counterbalance the renewed threat from Louisbourg, England set up an Atlantic bastion of its own. In 1749 a fleet bearing more than 2,500 new settlers from the British Isles began the construction of the city of Halifax.