The French and Indian War, or Seven Years' War, seems inevitable when we look at the big picture. It was the culmination of a series of violent conflicts between the French and English that had been occurring on and off for generations over hegemony in North America.
One reason for this war was economics. North America was full of riches. Furs from the interior, cod from the offshore fishing grounds, and sugar from the Carribean Islands were making both imperial powers immensely wealthy. However, if one could force the other out of the region, they would have a potential monopoly over these resources.
The French and British also had made numerous alliances with various native groups. These different tribes did not always get along with each other either. A complicated and entangling system of alliances frequently brought allies of the two empires into conflict with each other. This made the situation in North America very unstable and was a factor that led to the outbreak of conflict.
Another main reason for the conflict was a disagreement over who could lay claim to the Ohio territory. Most British settlements were east of the Appalachian Mountains and the French were mostly along (and north of) the St. Lawerence River. Few Europeans had made significant incursions into the Ohio River Valley, yet both Empires arbitrarily laid claim to it. Such a situation was untenable, and when the French military moved in to make a real claim to the land, the British were forced to respond in kind.