Explanation: The Union decided to invade Florida to take over the state and set up a Federal government.
IN the winter of 1863-64 Florida was an inviting field to Union aggression. The few Confederate troops left in Florida were scattered over the vast extent of territory they gallantly sought to defend, and it appeared that a strong body of Union soldiers could with little opposition advance into the center of the heart of Florida, expel the regularly constituted authorities from the capital, and organize a quasi-State government which should recognize the supremacy of the United States. In a letter to Gen. Gilmore, commanding on the coast, dated January 13, 1864, President Lincoln authorized such a proceeding on the ground that "an effort is being made by some worthy gentlemen to reconstruct a loyal State government in Florida," and he sent his private secretary, Mr. John Hay, with "some blank books and other blanks to aid in the reconstruction."
Almost simultaneous with Maj. Gen. William T. Sherman's Meridian Campaign was another Union expedition into the interior of Florida. Believing that northern Florida contained a large number of Unionists whom he hoped to see form a loyal reconstruction government, Pres. Lincoln authorized Maj. Gen. Quincy Gillmore, commanding the Department of the South, to send an expedition into Florida to liberate Unionists and slaves, and to cut the Confederate supply line.
Accordingly Gilmore, on February 5th, ordered. Gen. Truman Seymour to proceed with a division of troops from Hilton Head to Jacksonville. Adm. Dahlgren sailed with a squadron of 5 gunboats to escort the transports, and the expedition of about 7,000 men,including cavalry, infantry and artillery, was landed at Jacksonville on February 7, 1864. Like Sherman's expedition, Seymour's encountered Confederate cavlry and skirmished frequently as it advanced westward through northern Florida.
On the 20th, however, at Olustee, Brig. Gen. Joseph Finegan and his 5,000 Confederates attacked Seymour's 5,500 Federals. In a hard fought battle, also known as the Battle of Ocean Pond, Finegan was victorious and Seymour began a retreat back to the Atlantic coast. Total Union casualties were 1,861 and Confederate, 934. The battles of Okolona and Olustee were minor, almost to the point of triviality, and did not have any impact at all on the outcome of the war. Nonetheless, many Confederates at the time considered them, along with the Meridian Campaign, during which they feared Sherman intended to go all the way to Montgomery or Mobile, as great victories that portended the final success of Confederate arms.