In this case, Sherman had a plan all thought out, of course.

He meant to destroy the two remaining railroads in that part of the country, and that would finish up that region.

But General Hood did not play the military part that he was expected to play.

On the contrary, General Hood made a dive at Chattanooga.
This left the march to the sea open to Sherman, and so after sending part of his army to defend and hold what he had acquired in the Chattanooga region, he was perfectly free to proceed, with the rest of it, through Georgia.

He saw the opportunity, and he would not have been fit for his place if he had not seized it.
"He wrote me" (the General is speaking) "what his plan was, and I sent him word to go ahead.