The accidents of history and the facts of geography combine to form a delicate balance between English, French and Spanish interests in North America during the 18th century. The Spanish came to Mexico on a quest for gold after landfall in the Caribbean. The search for the Northwest Passage sent the French up the St Lawrence River to establish a royal province based on trade in furs. A wish for overseas settlements prompts the English to found colonies down the eastern seaboard.
Geography plays a rigid role in keeping the three national interests distinct and separate at first, while there seems to be room for all.
The natural direction for Spanish expansion is northwards, to the west of the Rockies, what is now New Mexico, Arizona and California. The French, from their base in the Great Lakes, are drawn south along the rivers that drain into the Mississippi. The English enjoy a fertile coastal fringe, neatly confined to the west by the curving line of the Appalachian Mountains.
All three colonial groups must conduct an argument with occupants of the land—the American Indians. During the first two centuries of colonization the Europeans have little more than skirmishes with each other, and these occur mainly at sea.
The situation changes dramatically in the 18th century. The main clash is between the French and the English. The two nations are at war with each other in Europe almost constantly from 1689. This is reflected in relationships between their neighboring American colonies.
But a more direct cause for conflict in North America comes from the interest of each colonial group in the Ohio valley. To the French this region is the first route southwards, running west of the Appalachians. To the British it is the first region available for expansion beyond the Appalachians. It is steadily encroached upon by English colonists, eager for new territory in which to trade and settle.
The sensitive nature of the Ohio valley becomes evident in 1749, when a French official is sent down the river to set into the landscape, at regular intervals, embossed lead plates stating the ownership of the land. They declare that it belongs to the king of France.
Source: History of North America: Three Slices of America
Gascoigne, Bamber. “History of North America” HistoryWorld. From 2001, ongoing.