Complex sentence: The French commander of the fort, Louis Du Pont Duchambon de Vergor, being outnumbered more than four to one, realised that his position was untenable, and moral in the fort deteriorated considerably once word was received that reinforcements would not be arriving from Fortress Louisbourg.
Split into simpler sentences: The French commander of the fort, Louis Du Pont Duchambon de Vergor, being outnumbered more than four to one, realised that his position was untenable. Moral in the fort deteriorated considerably once word was received that reinforcements would not be arriving from Fortress Louisbourg.