What exchange took place between lords and vassals under the feudal system?

Under the feudal system, lords provided vassals with fiefs (which were pieces of land) in exchange for military protection, loyalty and support. In order to do their duties and obtain the priviledge, vassals had to swear on oath loyalty to a particular lord at a feudal ceremony.  

A. They helped win the Battle of Santiago  in Cuba.

Explanation:

After the Spanish naval force was practically destroyed near Santiago de Cuba the U.S. Navy was recognized as one of the leaders in the world after this battle. But the Americans were reminded of the disorganization and low accuracy of firing at the beginning of the battle. The victory of the US forces succeeded in winning only because of the apparent superiority of the human forces and the almost complete lack of military training of the Spanish fleet.

A few days later the bombing of Santiago began. Among those who had the main in the siege where the Rough Riders. After the strong siege the city surrendered. In total, 24,000 Spanish soldiers surrendered in the south of the island. As early as August, the US military, along with the Cuban rebels, had completely captured Cuba.