The correct answer to this open question is the following.
The natural feature that made moving the British army for the Atlantic coast to the Ohio river valley so difficult was the Appalachian Mountains.
We are talking about a moment during the "French and Indian War," in the North America territory in which France and Great Britain fought over territorial interests in the Americas. Years later, this conflict derived in the "Seven Years War," in which other European nations intervened such as Prussia and Spain.
One problem the British troops had when trying to get to the Ohio River was the big Appalachian Mountains, a chain of mountains in the eastern part of the United States, that represents a natural barrier if you travel from the east to west of the country.