It preserved the Union
Although the Civil War was a traumatic episode in the history of the United States, it allowed the solution of irresolvable problems since 1776: it succeeded in abolishing slavery and reuniting the different states into a single, indivisible nation.
During the four years that this war lasted, more than 3 million men were mobilized and casualties reached the figure of 617,000, that is, 2% of the contemporary population. The North lost 359,000 men and the South 258,000. There were more deaths due to epidemics and diseases than to the war itself. To this must also be added the tens of thousands of civilian victims. This conflict is, along with the Second World War, one of the bloodiest in which the United States has participated.
Regarding the development of the country, before and after the war, we can affirm that as a final result, the US was considered one of the most powerful nations of the time and the armament lift of the moment greatly helped its performance during the future world wars.