We can point out some significant events that happened prior to President Lincoln, who was elected in 1860, signed the Pacific Railroad Act, such as:
The Southern secession - Separation within the Democrat party into northern and southern sectors. This event contributed to the success of the republican party of Lincoln and was the direct cause of the secession;
Civil war begins - Lincoln made it clear that secession was unconstitutional and the war came when the federal government tried to resupply forts in the South.
July 1861 - First Battle of Bull Run (Manassas)
July 1862 - Peninsular campaign
April, August, September 1862 - Battles of Shiloh, Second Bull Run, and Antietam