Final answer:
The main reason for the decrease in the number of soldiers after the Civil War involved demobilization driven by political pressure, technological advancements, and the shift to peacetime needs. Post-conflict periods usually see a substantial reduction in military personnel, as large standing armies are not necessary and entail high maintenance costs.
Step-by-step explanation:
The main reason for the decrease in the number of soldiers since the Civil War is due to demobilization efforts post high-intensity conflicts, changes in military strategy, technological advancements, and political factors, as evidenced after World War II when U.S. military forces were reduced from 12 million to 1.5 million due to political pressure and the reduction in demand for a large standing army during peacetime.
The transition from wartime to peacetime often involves a significant demobilization of military forces. After the Civil War, similar to the post-World War II period, political pressure and practical considerations led to a significant reduction in military personnel. Factors influencing this decrease included the immense cost of maintaining a large military, the advent of new technologies that made some roles obsolete, and the intense societal demand for returning to normalcy, including soldiers yearning to return home. Additionally, as with World War II, political decision-makers like President Truman felt constrained by public sentiment to reduce military strength despite strategic concerns posed by military advisors. Conscription laws enacted during the Civil War show that the desire for large armies fluctuated with the times, dependent on the level of national conflict and the willingness of men to serve. With each subsequent conflict, varying degrees of public opinion, technological progress, and economic consideration continue to shape the size and composition of armed forces.