Garibaldi deeply disliked the Sardinian Prime Minister, Camillo Benso, Count of Cavour. To an extent, he simply mistrusted Cavour's pragmatism and realpolitik, but he also bore a personal grudge for Cavour's trading away his home city of Nice to the French the previous year. On the other hand, he felt attracted toward the Piedmontese monarch, who in his opinion had been chosen by Providence for the liberation of Italy. In his famous meeting with Victor Emmanuel II at Teano on 26 October 1860, Garibaldi greeted him as King of Italy and shook his hand. Garibaldi rode into Naples at the king's side on 7 November, then retired to the rocky island of Caprera, refusing to accept any reward for his services.  At the outbreak of the American Civil War (in 1861), Garibaldi volunteered his services to President Abraham Lincoln. Garibaldi was offered a major general's commission in the U. S. Army through the letter from Secretary of State William H. Seward to H. S. Sanford, the U. S. Minister at Brussels, July 17, 1861. On September 18, 1861, Sanford sent the following reply to Seward:  He [Garibaldi] said that the only way in which he could render service, as he ardently desired to do, to the cause of the United States, was as Commander-in-chief of its forces, that he would only go as such, and with the additional contingent power--to be governed by events--of declaring the abolition of slavery; that he would be of little use without the first, and without the second it would appear like a civil war in which the world at large could have little interest or sympathy.  These conditions could not be met. On August 6, 1863, after the Emancipation Proclamation had been issued, Garibaldi wrote to Lincoln, "Posterity will call you the great emancipator, a more enviable title than any crown could be, and greater than any merely mundane treasure".  On 5 October 1861 Garibaldi set up the International Legion bringing together different national divisions of French, Poles, Swiss, German and other nationalities, with a view not just of finishing the liberation of Italy, but also of their homelands. With the motto "Free from the Alps to the Adriatic," the unification movement set its gaze on Rome and Venice. Mazzini was discontented with the perpetuation of monarchial government, and continued to agitate for a republic. Garibaldi, frustrated at inaction by the king, and bristling over perceived snubs, organized a new venture. This time, he intended to take on the Papal States.

Answer this question "How long did he serve with the forces?" by extracting the answer from the text above.
These conditions could not be met.