The Spanish-American War resulted in the United States becoming an overt imperialist country, conquering and taking possession of culturally alien lands. The result was that America itself was forever transformed. It will never again be the nation it was and it is not clear that, despite the homage paid to its founding, it will survive as a republic with a common consensus of values. Diversity is not consistent with unity.
It could be argued that the US forever transformed those alien lands as well. For example, some of the best, most patriotic Americans I know today are of Filipino heritage. Having them here in this country has been a major benefit if you ask me.
Crucial point
We became an Empire
Interesting documentary about the events leading up to the blast as well as the reverberations afterwards
https://www.youtube.com/watch?v=9nv87SNtCWs