Final answer:
Spain and France withdrew from British North America after ceding most of their territories to the British following the French and Indian War, which ended with the Treaty of Paris in 1763. This marked the end of French colonial power in North America and diminished Spain's influence in the future United States. Britain's dominance followed, allowing for an expansion of British territory and later the rise of the United States.
Step-by-step explanation:
Why Would Spain and France Withdraw from North America?
Spain and France withdrew from areas of British North America following a series of conflicts, including the French and Indian War, part of a larger global conflict known as the Seven Years' War. France lost the war and with the signing of the Treaty of Paris in 1763, they ceded most of their North American territories. France was left with only some Caribbean islands, while Spain lost northern Florida but received Louisiana in compensation. This treaty marked the end of French colonial power in North America, and although Spain retained significant territory in the southwest and the Louisiana region, its influence in what later became the United States was reduced. The rise of British dominance in North America led to the withdrawal of the Spanish and French from those areas that would be associated with the future United States.
Earlier, both Spain and France had aimed to challenge British power; Spain by joining forces with France during the war, and France by establishing trade and colonies in regions like Florida to counter British influence. Nevertheless, with the signing of the treaty, Spain's and France's territorial ambitions were curtailed, allowing the British Empire to expand its territory from Canada to Florida. The diminishing power of Spain and France in North America, combined with the subsequent rise of the United States, eventually led to the complete change in control of the continent.