Why did Washington bring troops to the Ohio River Valley in March 1754?

This was during one of the "Hundred Years Wars" between France and England. France had begun colonizing the New World first by creating fur trade outposts in Quebec and Acadia. Later, England had begun creating tobacco plantations and granting royal charters to colonies that expanded all the way up to New England. By the 1750s, both France and England claimed the areas that served as a barrier between New France and New England. These areas were Acadia (by the coast) and the Ohio River Valley (inland).

Up until 1754, most of the fighting in this area was a proxy war between Native American allies. The French had originally built strong relationships with Algonquin speaking groups, which put them at odds with the Iroquoian speaking groups. When England began colonizing, they fought early and often with the Algonquins as far south as Virginia. Eventually, this cemented the Iroquois as allies to the British, and the Algonquin as allies to the French.

The two Native American groups were forced to fight each other for access to furs in the Great Lakes region, as they had become dependent on trade with their European allies. While these "Beaver Wars" lasted a long time, in the mid 1700s, New England was expanding further west, prompting Britain to increase the pressure on France to give up their claim to the territory. Washington was sent to take a fort in`the Ohio River Valley, which sparked the French and Indian War.