Actually the Civil War is what made America a superpower.
The American Civil War, fought from 1861 to 1865, was a pivotal event that profoundly shaped the trajectory of the United States towards becoming a global superpower. The conflict not only settled the issue of secession but also ushered in significant economic, social, and political changes. Economically, the war spurred industrialization and innovation, particularly in weaponry and infrastructure, laying the foundation for America’s future industrial might. Socially, it marked a transformative period with the abolition of slavery, albeit with ongoing struggles for civil rights. Politically, the Union victory reinforced the supremacy of the federal government and strengthened national unity. These developments set the stage for America’s rapid expansion and influence on the world stage in the decades that followed, as the nation transitioned into a burgeoning industrial power with a unifying identity and expanding global ambitions.
What you said - that, before the civil war, the war with Mexico, and the whole westward expansion and the making of a continent wide nation, made what industrialization there was easier to expand, coast to coast, than was Europe able to do because of all the political divisions there, and the strong rivalries and disagreements among them. After that it was the war with Spain and the U.S. acquisition of a real colony, the Philippines, that made the U.S. a global power with global reach.