Question

The "Rough Riders" (pictured here) were instrumental in the US victory against

Answer 1

The "Rough Riders" was the name given to the First U.S. Volunteer Cavalry under the leadership of Theodore Roosevelt. They were volunteers in the US Army who fought in the Spanish-American War.

Answer 2

The rough riders can be given to u.s volunteer cavalry under the leadership of a Theodore Roosevelt.

The war can be happened between us army and Spanish people.  

They both were fight with each other.

And the volunteers in us army can be fight with Spanish American war.

And they can fight each other country.

So the war happens for both countries.