His political beliefs greatly influenced his decision to serve in the Union Army during the American Civil War.

Willich returned to the United States and lived the remainder of his life quietly in Ohio until his death in 1878.

With an elder brother, Willich found a home in the family of Friedrich Schleiermacher, a theologian, whose wife was a distant relative.

Willich tendered his resignation from the army in a letter written in such terms that, instead of its being accepted, he was arrested and tried by a court-martial.

The pistol duel was fought in Belgium with Barthélemy acting as Willich's second;[9][note 1] Schramm was wounded but survived the encounter.

[10][11] Coming to the United States in 1853, Willich first found employment at his trade in the Brooklyn Navy Yard.

In 1858, he was induced to go to Cincinnati as editor of the German Republican, a German-language free labor newspaper, which he continued until the opening of the Civil War in 1861.

[6] Willich became known as one of the "Ohio Hegelians" (followers of German philosopher Georg Wilhelm Friedrich Hegel), along with John Bernhard Stallo, Moncure Daniel Conway, and Peter Kaufmann.

With the outbreak of the Civil War in early 1861, Willich actively recruited German immigrants in the southwestern Ohio region.

He joined the 9th Ohio Infantry ("Die Neuner") as regimental adjutant with the rank of first lieutenant, and was promoted to major in August of that year.

An innovative officer, he suggested construction of special wagons convertible to pontoon boats by removal of wheels.

Though his superiors rejected both ideas, Willich's concern for his men's well-being earned him the nickname "Papa".

Rewarded by a promotion to brigadier general of volunteers in July 1862, Willich fought at the Battle of Perryville under Maj. Gen. Don Carlos Buell in Kentucky.

He received a brevet promotion to major general of US Volunteers on October 21, 1865, then resigned from the army to return to civilian life.

It rankled the German-American soldier that General Joseph Hooker had blamed German troops of the 11th Corps for his defeat at Chancellorsville.

Of the remaining 5,000, only one-third were German, these having been the units offering the stiffest resistance to the Confederate attack made by Stonewall Jackson.

He stayed in Germany long enough to receive a college degree in philosophy, graduating from the University of Berlin at the age of sixty.

In his concluding note to the Revelations Concerning the Communist Trial in Cologne, Marx wrote: "In the Civil War in North America, Willich showed that he is more than a visionary".