His father, an officer of the Prussian Army, died in poverty during the French occupation of the Kingdom of Prussia (see Napoleonic Wars), and the young Roon was brought up by his maternal grandmother.

[1] Roon entered the corps of cadets at Kulm (now Chełmno, Poland) in 1816, from where he proceeded to the military school at Berlin in 1818, and in January 1821, he received a commission in the 14th (3rd Pomeranian) regiment quartered at Stargard in Pomerania.

[2] In 1832, Roon published the well-known Principles of Physical, National and Political Geography, in three volumes (Grundlage der Erd-, Völker- und Staaten-Kunde), which gained him a great reputation, and of which over 40,000 copies were sold in a few years.

[1] In 1832, Roon rejoined his regiment and was afterwards attached to the headquarters of General von Müffling's corps of observation at Krefeld, where he first became aware of the very inefficient state of the Prussian Army.

In 1842, after an illness of two years brought on by overwork, he was promoted to major and attached to the staff of the VII Corps, where he was again impressed with the inefficiency of the organization of the army, and he occupied himself with schemes for its reform.

During the disturbances of that year, he served under Prince William, later king and emperor, in the suppression of the insurrection at Baden and distinguished himself by his energy and bravery, receiving the 3rd class of the order of the Red Eagle in recognition of his services.

In 1850, after the revelation of defective organization and efficiency that led to the humiliating Treaty of Olmütz, Roon was made a lieutenant-colonel and, in 1851, full colonel.

[3] Roon, by contrast, believed that the Landwehr was both a politically and militarily false institution, limited in utility and lacking martial qualities.

Roon's proposals for army reorganization met with strong opposition from the Prussian Landtag, which was dominated by the liberal German Progress Party, which wanted parliamentary control over the military budget.

It took years of political fighting and the strong support of the new prime minister, Otto von Bismarck and Moltke, before Roon carried the day.

[4] After the successful outcome of the Second Schleswig War of 1864, Roon went from being widely disliked in Prussia to a national hero in still-disunited Germany.