 Complete the following phrase:  The traditional method of dealing with an armored breakthrough was to pick away at its sides, forcing it to maneuver away in order to find less-defended areas of advance. If these spoiling attacks can be set up on both sides of the route of attack, the armored spearhead is forced into an ever-decreasing frontage, eventually being pinched off and losing the ability to maneuver. The classic example of a successful anti-Blitzkrieg was during the 