When did the result of the US Civil War become inevitable?

Concerning the US Civil War, historians are cautious about naming the result of any battle that then made the outcome of the War inevitable. Of course this discounts the obvious, such as the fall of Richmond or the Robert E. Lee surrender to US Grant. Historians all armed with the same set of facts have all expressed different opinions as to why and when the outcome of the war was inevitable.Based on all information many people have read, it appears that the reelection of US President Lincoln was a point in time where time for the South became limited. Ironically, Lincoln's first election and his last election mark the beginning and end of the War.