Both France (in Quebec) and England had settlements in the Ohio Valley, and each sought to control the resources there (fur, timber). Caught in the middle were the Indians (Native American tribes), who sided mostly with the French because the English settlers were building permanent settlements on their lands.
Britain and France were rival countries, and always fought for supremacy. Also, both countries believed that some of the area was owned by them. Plus, the British saw the French land being controlled by the Roman Catholic church as a threat to their religious freedom. And finally, the New World had enormous possibilities politically, socially, and especially economically.
The French would not let English colonists settle in the Ohio River valley.