Final answer:
The Guano Islands Act was important because it provided exclusive rights to the guano recovered and allowed the United States to gain control over valuable guano islands. Guano was a valuable source of fertilizer used in agriculture.
Step-by-step explanation:
The Guano Islands Act was important because it provided an incentive for American sailors to find and claim undefended islands for America by giving the discoverer exclusive rights to the guano recovered.
The act allowed the United States to gain control over valuable guano islands, such as parts of the Hawaiian chain, Midway Atoll, and American Samoa.
Guano, which is the droppings of seabirds, was highly profitable as it was a valuable source of fertilizer that was used in agriculture.