What does textbook author Alan Brinkley allude to in mentioning “middle ground” in his introduction?

Alan Brinkley was an American political historian who taught for over 20 years at Columbia University. He was the Allan Nevins Professor of History until his death. From 2003 to 2009, he was University Provost.

Explanation:

this forms a narrow, steep sided inlet (sometimes deeper than 1300 metres) connected to the sea. the terminal moraine pushed down the valley by the glacier is left underwater at the fjord’s entrance, causing the water at the neck of the fjord to be shallower than the main body of the fjord behind it.

did you check the study guide?