The primary reason the war began was a dispute between the French and English over the border between their respective territories in the Ohio River Valley. British settlers had begun moving into the territory claimed by France primarily for firs. Additionally, a number of British interests, including the Ohio Company, laid claim to 200,000 acres, hoping to sell it later for a profit. The French used this to their advantage to woo the Indians and alienate any relationship between the British and the Indians. One French trader told a group of Indians

The English are much less anxious to take away your peltries than to become masters of your lands.

The French then buried plates in the soil which stated that the land was French soil. This created a problem for the British, as if they accepted the French claim, British North America would be sandwiched between French America and the Atlantic, a mere strip of land on the Atlantic coast.

The British considered the French action a trespass and in Spring, 1754 sent George Washington, then a 28 year old colonel into the area to drive away the French. A brief skirmish followed during which the French commander, one Joseph Coulon de Villiers de Jumonville, was wounded. Under a flag of truce, Jumonville indicated a letter in his pocket would clear up the whole matter. The letter essentially stated that the land was the property of France. When Washington turned to have his interpreter read the letter, an Indian in his group named Tanaghrisson, but called the "Half-King" by the British went up to Jumonville, said in French Tu n'est pas encore mort, mon pere ("Thou art not yet dead, my father) and buried his hatchet in the Frenchman's skull, after which he washed his hands in brain tissue. This was a signal to the other Indians with Washington who killed all the Frenchmen but one. Washington was forced to make a quick withdrawal before a larger French contingent arrived and erected a small fort, named Necessity, but was soon forced to surrender it. The ensuing battle in which Washington's commander, General Braddock, was killed, marked the first battle of the war.

Why did France and Britain fight in the French and Indian War? 

Let's focus our discussion on the French and Indian War.

The French and the British were involved in a worldwide conflict from 1756-1763. This conflict was known as the Seven Years War. The part of the Seven Years War that was fought in North America was called the French and Indian War. The French and many Native American tribes fought against Great Britain.

The French and Indian War was fought for a few reasons. One reason was for control of the lucrative fur trade in the Ohio Valley. The French had established a firm control over this trade with the Native Americans. As the British began to expand their settlements in North America, the French became concerned that the British were going to try to take away or reduce the fur trade that France had with the Native Americans.

Another reason was for control of land. Both Great Britain and France were rivals. If one country could win the war, they would become stronger at the expense of their rival. The winner of this war would likely get land from the country that lost the war. After the French and Indian war ended, the British got much land from France. Great Britain got all of France’s land east of the Mississippi River except for New Orleans. As a result, France was out of North America, which was a positive development for France’s rivals, Britain and Spain.