In 1861, he was one of the chief editorial writers on the
New York Tribune and the author of the controversial "On to Richmond" articles after the
First Battle of Bull Run. He returned to Iowa following First Bull Run and, as
Colonel, helped to raise the
1st Regiment Iowa Volunteer Cavalry. On July 18, 1862, President
Abraham Lincoln appointed Warren to the grade of
brigadier general of volunteers, to rank from July 16, 1862, with a command in the army in
Missouri under
Major General Samuel R. Curtis. In 1863, General Warren was the leading candidate before the Republican State Convention for
governor of Iowa, but by a combination of the supporters of other candidates, Warren was defeated. On February 21, 1866, President
Andrew Johnson nominated Warren for appointment to the grade of
brevet major general of volunteers, to rank from August 24, 1865, and the
United States Senate confirmed the appointment on April 26, 1866. Warren was mustered out of the volunteers on August 24, 1865. ==Postwar career==