The Spanish-American War was fought in 1898 and was an imperial conflict. The major combatants were the United States and Spain. The war was fought on two fronts: Cuba and the Philippines. The war was instigated by Cuba and the Philippines in an effort to gain their independence from Spain. Jose Marti was the leader of the Cuban independence movement. In the Philippines Andres Bonifacio and Emilio Aguinaldo led an independence movement through Katipunan, the organization they founded. The United States intervened on both countries behalf as public pressure for intervention mounted.

The United States also had an imperial interest in intervention. At the conclusion of the war, the Americans annexed Puerto Rico, Guam, and the Philippines as spoils of victory. They also gained a strong economic and political foothold in Cuba.

Combatants of the Spanish-American War:

• United States
• Philippines
• Cuba
• Katipunan
• Guam 
• Puerto Rico

The only countries (that were countries at the time) involved in the Spanish-American War were Spain and the United States.  These two countries fought and the result of the war was a change in the control of two places that are now independent countries.

The Spanish-American war was caused in large part by a desire on the part of America to aid Cubans who were fighting for independence from Spain.   Cuba was at that time a colony of Spain and was trying to gain its freedom.  The same is true of the Philippines.

So, the war involved four places that are countries today, but only two of those were actually countries at the time of the fighting.