France and Britain were international rivals seeking wealth and power. This competition extended to their colonies in North America, and allowed the two countries - as well as Spain, The Netherlands, even Sweden - to fight each other overseas without formally declaring war and risking invasion of the homelands in Europe.
The French and Indian War was a war fought by proxy through Native Americans, who were forced to ally with either England or France. The war was one of a continuing chain of conflicts in North America, stretching back more than a century. Some wars were fought between Native Americans vs. colonists and others between the colonists of different European nations.
The French strategy was to create trading stations to acquire furs from Native Americans, in contrast to the English strategy to flood the colony with Protestant immigrants who would be loyal to England in any fight with Spain/France. The failure of the French to establish colonies on the Atlantic seaboard south of the Saint Lawrence River, and their slow occupation of the Ohio River and Mississippi River valleys, ultimately allowed the English to gain control of the North American continent.
In 1753, the French established military bases on the southern edge of Lake Ontario and in what today is northern Pennsylvania. In late 1753, Lord Dinwiddie sent George Washington to notify Legardeur de St. Pierre at Fort de la Rivière au Boeuf that the French had encroached into territory claimed by the English. Part of the English claim to the Ohio River territory was based on the 1744 Treaty of Lancaster. After the Iroquois supposedly "sold" their claim to that land, the Ohio Company obtained a land grant to much of what is modern-day Ohio.
After Lord Dinwiddie gave Washington the assignment to travel to Fort Le Boeuf, Washington hired Christopher Gist to serve as his guide. Together with Indian allies, the two Virginians reached the French headquarters near Lake Erie (modern-day New Waterford, Pennsylvania) despite the November snow and ice.
the English claim to the Ohio River Valley was portrayed in John Mitchell's 1755 map
Source: Library of Congress, A map of the British and French dominions in North America, with the roads, distances, limits, and extent of the settlements
Washington was treated well by the French at Fort Le Boeuf. The officers must have appreciated the opportunity to converse with a "gentleman" in the middle of nowhere - but they rejected Dinwiddie's claim that the Ohio River was British territory. Washington's tiny party in 1753 was clearly inadequate for anything more than a brief scouting expedition, and to the French any military threat from Williamsburg must have seemed minor. The French were more concerned with the Native American allies that accompanied Washington and Gist, and worked hard to shift the Native American loyalties to the French.
Washington hurried back to Williamsburg from Fort Le Boeuf in order to alert Dinwiddie as fast as possible, surviving a dunking in an ice-filled river and an attempt to kill him by a Native American in his traveling party. Washington submitted a written report to Lord Dinwiddie, who sent it to London. The report was published as The Journal of Major George Washington, and the 21-year old Virginian gained his first recognition in Europe through that report from the frontier.
In 1754, the Virginia colony sent reinforcements to a fort that colonists were building at the Forks of the Ohio, to protect it from the French. However, before the Virginians arrived, the French captured the fort and renamed it Fort Duquesne, one of several they planned along the Ohio River to connect "New France" in Canada with their holdings in Louisiana. Colonel Joshua Fry was the leader of the Virginia expedition, but Fry died before getting to Pennsylvania. The second-in-command, George Washington, assumed leadership of the military force - and led it into a debacle.
After learning the fort had been captured and the Virginia colonists evicted, Washington attacked a group of Frenchmen in late May, 1754 while they slept. The site of the attack is now called Jumonville Glen, named after the French leader who died in the British ambush. After the Virginians had captured or killed all the Frenchmen, one of Washington's Native American allies took a hatchet and bashed out the brains of de Jumonville. This murder of the French leader, after he had surrendered, guaranteed continued hostilities between the Europeans trying to occupy the Ohio River valley.
The French responded by sending troops and Native American allies from Fort Duquesne to confront Washington's small force. Washington failed to maintain good relations with his Native American allies, and they deserted the Virginians. Washington built a small fort with a palisade around it in an open field, called Fort Necessity, but was forced to surrender after less than one day of fighting. Washington signed a surrender document, written in French, in which he admitted to "assassinating" the French ambassador who had travelled from Fort Duquesne to meet with the Virginians.
What today we call the French and Indian War may have been inevitable, once two European powers sought control over the same Ohio River land. The war was triggered by the actions of the military force led by Washington in 1754, but had Washington not been in charge of the Virginia response to the French incursion then a war would have been triggered by some other incident in the 1750's.
The war was inevitable... but the role of the Virginians was not. Why were the Virginians fighting the French so far from the boundaries of the Virginia colony? Jumonville Glen, Fort Necessity, and Pittsburg (Fort Duquesne/Fort Pitt) are all in Pennsylvania - why didn't the Pennsylvanians fight the initial battles?
Land-hungry Virginians in the General Assembly and on the governor's Council launched the Ohio Company in 1748. The average Virginian without a massive land grant shared the hunger for land, and was willing to fight Native Americans, the French, or even Pennsylvanians to obtain cheap land. The Quaker-led assembly in Pennsylvania lacked the avarice and willingness to fight for land. The Virginians saw an opportunity to gain control over the Ohio territory, and had no qualms about citing the colonial charters as the basis for their land claims or raising an army to fight for that land.
When Lord Braddock arrived in 1755 to lead the British army to the capture of Fort Duquesne, he established his base of operations in Alexandria - not Philadelphia. Farmers bringing crops and other supplies to Braddock created "Braddocks Road" in Loudoun and Fairfax counties, but Braddock marched up modern Route 7 and through Maryland to what is today Cumberland, Maryland.
From Cumberland the English cut a road through the wilderness to Fort Duquesne. However, Braddock was killed and the British defeated in a surprise assault by the French and their Native American allies near the fort. Much to the dismay of the Virginians, however, the British forces moved to Philadelphia after Braddock's defeat and went into "winter quarters" in mid-summer of 1755.
Even worse, the British determined to attack Fort Duquesne by building a road through the Pennsylvania wilderness, enhancing the economic link between Philadelphia and the Ohio River in the process. After the British captured Fort Duquesne and renamed it Fort Pitt, the Virginia investment in fighting the French ended up providing advantages to the Pennsylvania colony rather than to Virginia. The Virginians even dropped their claims to the land in southwestern Pennsylvania, though the land claims already established by Virginia colonists were confirmed by the Pennsylvanians.
General Braddock knew the details of Fort Duquesne, thanks to a diagram and report smuggled out by an English hostage retained after the surrender of Fort Necessity
Source: University of Pittsburgh, Robert Stobo to Colonel Innes, July 28, 1754
the English planned to seize four major forts in the 1755 campaign, isolating Quebec and Montreal
Source: ESRI, ArcGIS Online