Complex sentence: In 1869, James Jennett claimed the island for the US under the Guano Islands Act of 1856, but in 1972 a treaty was signed (ratified in 1981) which ceded U.S. claims to the island to Colombia.
Split into simpler sentences: In 1869, James Jennett claimed the island for the US under the Guano Islands Act of 1856. In 1972 a treaty was signed (ratified in 1981) which ceded American claims to the island to Colombia.