"The outbreak of the American Civil War found him in the employ of the Southwestern Telegraph Company [(later Western Union)] in Alabama, and he was absorbed with it into the Confederacy.

There was no getting away, and he was transferred to Nashville, Tenn."[3] While in Alabama, he had transcribed the speech in which Jefferson Davis vowed to “carry the sword and torch through the northern cities” and sent it to the Associated Press.

[5] A brief visit to his family in Cleveland followed, after which he enlisted in the United States Army Telegraph Corps, staying with General John C. Frémont throughout his West Virginia campaign.

While serving at the White House telegraph office, Rosewater was responsible for sending out President Abraham Lincoln's "Emancipation Proclamation" on January 1, 1863.

Rosewater married Leah Colman on November 13, 1864 in Cleveland, Ohio, departing after the wedding for Omaha, Nebraska where he had secured a home for his new bride.

A period review of his writing style commented that he wrote "concise, pointed, and clear, and in political campaigns, especially, he is an untiring and dauntless fighter.

[9] Rosewater constantly pursued his own version of news, and often got into confrontations, with one even being given front page treatment in The Day's Doings, a sensationalist New York City journal.

[17] During 1957 the Columbia Broadcasting System and the AJC produced a dramatic television show highlighting Rosewater's arrival in Omaha, his anti-slavery attitude and his journalistic style.