Most historians agree that the Union victory in the American Civil War was inevitable for the following reasons.
1) The economic superiority of the North in terms of manufacturing and food production.
2) The inability of the Confederacy to be recognized diplomatically by any of the major European Powers, specifically Great Britain.
3) The large slave population of the South which had to be controlled whilst defending territory against the various Union Armies.
4) The failure of political leadership in the person of Jefferson Davis.
5) The spectre of defending the institution of African Slavery which had been abolished 30 years before in most of the civilized world.
These are but a few of the reasons for the Union victory, but they are the ones almost every historian will agree on without argument.