Agreed. I think the Civil War transformed America to the level of world power. It may not have felt like it at the time but that is the war I would say changed everything. The subsequent wars were the manifestation of the changes the Civil War had wrought.
The US had enough power to demand that France leave Mexico immediately after the end of the US Civil War, but our Navy went into steep decline pretty much as soon as that war ended. So our ‘influence’ really didn’t extend past the Caribbean & Canada. Add in the expense of the military occupation odf the South (Reconstruction) and the US rrally wasnt quite ‘there’ yet. We were about were China is now. Big player on the local block but less so the further you get from the home turf.
The Spanish-American War & the building then sailing of the “Great White Fleet” showed the world we ha entered the international stage as a world power to be reckoned with. One maybe not the equal to a Great Britain but certainly on par with any continental European power. WW1 demonstrated we were the equivalent of Great Brtiain. (At the time I doubt the “talking heads” of the day realized what a hollow power GB was!) WW2 sealed the deal!
European countries were actually quite worried at the end of the Civil War. We had an army and navy more powerful than any other nation on earth. They thought we would engage in imperialistic conquest.