The part that did the practice of slavery the most was the South.
USA had a better navy. (The White Fleet?)
USA was backed by guerrlia warfare in the Philippines.
USA had terrible guns going against the Spanish in the San Juan hill.
The USA Springfield Gun 1892 - 99 side clip was highly inefficient compared to the Spanish Mauser.
The Spanish had more firepower the Maxim beat the Gattling Gun.