Short answers, pulled from the story.
The Union referred to the federal government of the United States from 1861 to 1865 and the unity of states within that constitutional framework. Loyal states resisted the secession of slave-holding southern states to form this political entity known as the North.
Abraham Lincoln oversaw supplies, finances, manpower, and the selection of generals during his presidency from 1861 to 1865. His cabinet included William Seward at State, Salmon P. Chase at the Treasury, and Edwin Stanton who took over the War Department from 1862 onward.
Copperhead Democrats formed a large faction opposing the war and demanding an immediate peace settlement throughout the conflict period spanning 1861 to 1865. Clement L. Vallandigham became the most prominent Copperhead leader as a congressman from Ohio before losing his election for governor in 1863.
By the end of 1861, 700,000 soldiers were drilling in Union camps across multiple states. The first wave served only ninety days before returning home or reenlisting for three years later.
More soldiers died from disease than from battle wounds during the American Civil War period spanning 1861 to 1865. Epidemics of chicken pox, mumps, whooping cough, and especially measles struck camps where thousands gathered together alongside dangerous new diseases like typhoid fever and malaria.