Short answers, pulled from the story.
Proclamation 80 was a presidential proclamation signed by Abraham Lincoln on the 15th of April, 1861, calling for 75,000 militiamen to suppress the Confederate rebellion. It was formally titled "A Proclamation by the President of the United States, the 15th of April 1861" and was countersigned by Secretary of State William H. Seward.
Lincoln based Proclamation 80 on the Militia Act of 1795, specifically sections that authorized the president to call forth militia when federal laws were obstructed by combinations too powerful for federal marshals to suppress. The act also required Lincoln to issue a proclamation ordering insurgents to disperse within a set time, which he set at twenty days.
Proclamation 80 called for 75,000 militiamen. That ceiling traced to a law passed on the 2nd of March, 1799, which capped the president's provisional army at 75,000 men. The number had never been revised despite U.S. population growing from roughly 5.3 million in 1800 to more than 31 million by 1860.
Governors of Arkansas, Kentucky, Missouri, North Carolina, Tennessee, and Virginia all refused to supply troops. Governor Isham Harris of Tennessee pledged to raise fifty thousand men to defend Southern rights instead. In contrast, northern states such as Indiana offered twice their requested quota, and Massachusetts volunteers arrived in Washington D.C. by the 19th of April.
The Proclamation stated that the first service assigned to the called forces would probably be to repossess forts, places, and property seized from the Union. It also pledged to avoid devastation, destruction of property, and disturbance of peaceful citizens, and it summoned Congress to assemble at noon on the fourth of July.
Under the Militia Act of 1795, no officer or private could be compelled to serve more than three months in any one year. State governors held more authority than the president to extend militia service beyond that period. Each regiment called under Proclamation 80 was ordered to consist of an aggregate of 780 officers and men.