Following the family tradition of his father and grandfather, Prussian officers both, Karl von Bülow also entered the army, fighting in the wars of both 1866 and 1870/71.
In the beginning of WWI, by then Colonel-General v. Bülow was given the command of the 2. Army and the supreme command of the 1. Army (v. Kluck). Captured the fortress of Namur (22-23 August 1914). Von Bülow defeated General Lanrezac's fifth Army at Charleroi (23-24 August), driving Lanrezac back a second time to Guise-Saint Quentin on 29-30 August. Von Bülow, anxious to close the gap between Second Army and Kluck's First Army on the west, ordered Kluck to turn toward him, and crossed the Marne on 4 September, but retreated as a result of the successful Anglo-French counterattack against Kluck at the Marne.
After the conquest of Namur (August 23/24.1914) and the victorious battle of St. Quentin (August 29/30.1914) v. Bülow's 2. Army overstepped the Marne (September 4.1914). On September 6.1914 the French and the British attacked the 1. Army. Colonel-General v. Kluck ordered two corps from his left to his right wing, causing the 30-40 kilometre wide gap formed between the 1. and 2. Army. Von Bülow ordered the retreat on September 9.1914 because he was afraid of a breakthrough and did not know the correct situation of the fighting corps. The Germans pulled back to the Aisne. The Allies called this battle the 'Wonder at the Marne' but the Germans called it a 'drama' and von Bülow was accused of the failure. But the German problems were rooted in the changes to the Schlieffen plan and they continued to affect the headquarters organisation in Luxembourg and actions of the Chief of the General Staff von Moltke II. On October 9/10.1914 the 2. Army was reorganized at St. Quentin.
After the battles of Le Quesnoy and Lihons, the front of the 2. Army was frozen. Von Bülow was appointed as Field-Marshal but in April 1915 he was retired owing to illness.
Bülow, Karl v., Mein Bericht zur Marneschlacht, Berlin: Scherl, 1919.
Blond, George, The Marne, London, 1965
Gebsattel, Ludwig v., Generalfeldmarschall Karl v. Bülow, Munich: Lehmann, 1929
Krack, Otto, Generalfeldmarschall von Bülow, Berlin: Scherl, 1916