What were the main reasons why the French and Indian War started?

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.