Here's my abridged history of Cuba. While we do not know much about per-Columbian Cuba, the island was inhabited by an Arawak tribe called the Taíno. After Christopher Columbus landed in 1492, things went downhill. The locals were enslaved by the Spanish and most died off following the waves of European diseases that the colonizer brought with them. Measles and smallpox were the main diseases that caused this disaster.
The Spanish used the island for plantations and as a colonial outpost, overseeing their colonial holdings in the western hemisphere. The 18th and 19th centuries brought European wars to the Caribbean island. These wars eventually inspired many Spanish holdings to revolt, including Cuba. After a bloody war the Spanish suppressed the revolt, just in time for the US Battleship Maine to be sunk.
In the April of 1898, The USS Maine exploded and sank in Havana's harbor. This event sparked the Spanish-American War. The outcome of this war led to an expansion of the United States' holdings in the Pacific and Caribbean, with the island of Cuba becoming a US protectorate. On May 20, 1902, Cuba was granted Independence. This is when the Guantánamo Bay Naval Base was first created.
Fast-forwarding to 1950's, Fidel Castro came into power, overthrowing the existing government, and forming a Soviet style communist regime. This did not sit well with the US. Since that time, thousands of refugees have made their way to the US, the Cuban Missile Crisis occurred, the Bay of Pigs was invaded, and Castro held that the United State's presence at Guantanamo Bay Naval Base was a violation of international law. Briefly under President Obama, relations with the Cuban Government were rebuilt, but those actions were undone by Donald Trump. And that's where we are today.
Guantanamo Bay Naval Base
When Cuba gained independence in 1901, Cuba's constitution included text from a bill in the US called the Platt Amendment. The Platt Amendment is what granted the US the land that would become the Guantanamo Bay Naval Base. For the privilege of our presence, the US pays $2000 in gold each year, although Cuba has not been collecting since Castro took control over the island.
The Guantanamo Bay detention camp was established towards the early years of the invasion of Afghanistan and Iraq, and it holds detainees who are accused of Terrorism. The operation of this detention center has been central to many complaints about the US government violating human rights by committing atrocities such as waterboarding. President George W. Bush referred to the practice as "Enhanced Interrogation" and most of the planet, including the United Nations refers to that practice as torture.
Today there are fewer than 50 detainees awaiting their trials.
For a longer and more thorough understanding, please check out Wikipedia's article.