To understand the heated debates surrounding hurricane relief aid for Puerto Rico, you have to understand the island's complicated history with the U.S.

Officially, Puerto Rico is autonomous but not sovereign. The island has a representative in Congress, and its people have U.S. citizenship, but they lack certain rights like voting in presidential elections. (See exclusive photos of the devastation in Puerto Rico.)

Before it was under U.S. control, Puerto Rico belonged to Spain, but that all changed during the late 19th century's Spanish-American War. Under the 1898 Treaty of Paris, Spain ceded Puerto Rico to the U.S. government, and by 1900 the U.S. had instituted a civil government on the island.

It was only two decades later that National Geographic photographer Charles Martin visited the island, in 1924, just seven years after Puerto Ricans were officially granted U.S. citizenship. Martin's images show the island in the early stages of its history as an American commonwealth, showcasing a thriving culture, gorgeous tropical landscape, and a growing economy.

In the photos, fields full of tobacco and sugar cane cover the island's hills. The crops were lucrative and made capitalists in Puerto Rico and the U.S. wealthy.

While many of Martin's images show an economically rising island, they also reminisce on Puerto Rico's Spanish past. Streets in old San Juan showcase Spanish colonial architecture popular during the 18th and 17th centuries. Even older still is Castillo San Felipe del Morro, a citadel built during the 16th century.

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The island was first taken under Spanish control after Christopher Columbus reached its shores in 1493, meaning, at the time of Charles Martin's visit, Puerto Rico was more Spanish than it was American. Today, the region's past has left it with an identity that's uniquely Puerto Rican, while the complex political ties to the U.S. established a century ago persist.

A complicated political future is likely still in store. The people of the island are conflicted—many want statehood, others want independence, and some would prefer to leave things just the way they are.