The recent history of American political prisoners released from Iran and North Korea

Trump: 'Honored' by release of US prisoners
Trump: 'Honored' by release of US prisoners

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(CNN)President Donald Trump proudly and dramatically welcomed home three Americans released after captivity by North Korea and ahead of a planned summit between him and the North Korean dictator Kim Jong Un.

Their release could help set the table for a fruitful Singapore summit between Trump and Kim as the US President seeks to discourage North Korea from its pursuit of nuclear weapons.
The move comes in tandem with Trump's decision to break the US out of an international agreement aimed at dissuading Iran's nuclear ambitions. At the time of the agreement between President Barack Obama, the government in Iran and other world powers, Obama was criticized for entering into a deal while Americans were still held in Iran. Some of those, like Washington Post reporter Jason Rezaian, have since been released.
    Trump's overtures to Kim undoubtedly helped secure the release of the three prisoners. His rejection of the deal with Iran could hurt efforts on behalf of the five Americans still held there.
    Political prisoners have long been used by governments in their political chess games; it's telling that so many of them in recent history have been held in either Iran or North Korea. CNN's library has a full list of detained Americans.
    Why these Americans were held in North Korea
    Why these Americans were held in North Korea

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    Why these Americans were held in North Korea 01:37
    Freeing prisoners from North Korea, in recent years, has largely required a high-level emissary of sorts.
    Secretary of State Mike Pompeo, the same person negotiating terms of the US-North Korea summit, went to Pyongyang to retrieve Kim Dong Chul, Kim Hak-song and Kim Sang Duk, who's also known as Tony Kim.
    Then-Director of National Intelligence James Clapper went to retrieve Kenneth Bae along with Matthew Todd Miller, both of whom were accused of "hostile acts." They were released in November of 2014 after spending months in a hard labor camp.
    An outburst on CNN by Dennis Rodman, who slammed Bae, then in prison, after the former basketball star met with Kim Jong Un, helped draw attention to Bae.
    Journalist Laura Ling speaks in front of Euna Lee, former Vice President Al Gore and former President Bill Clinton after Ling and Euna Lee arrive in Burbank, California after being released by North Korean authorities on August 5, 2009.
    The journalists Laura Ling and Euna Lee were freed after former President Bill Clinton traveled to Pyongyang in August of 2009 to ask for their release and to collect them.
    Other releases have had unhappy endings. The American student Otto Warmbier was released by North Korea in 2017 when he was in a coma. He died shortly after returning home.
    His family members attended the State of the Union address this year as Trump's guests.
    Trump: We honor Otto Warmbier's memory
    Trump: We honor Otto Warmbier's memory

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    Trump: We honor Otto Warmbier's memory 02:34
    All five currently detained Americans on CNN's list, now that the three have been released from North Korea, are in Iran. They were all detained after the Iran nuclear agreement was put in place in 2015 and they include an ailing father and son, Baquer and Siamak Namazi, who have been detained since February of 2016 and October 2015, respectively, and were sentenced to 10 years in prison. Baquer Namazi was temporarily released this year for four days due to ailing health. Reza Shahini was arrested in July of 2016 while visiting family in Iran. Karan Vafadari ran an art gallery in Tehran and was arrested along with his wife in December of 2016 and sentenced to 27 years in prison. Xiyue Wang is a Princeton graduate student who was sentenced in July of 2017 to 10 years in prison.
    Freed reporter Jason Rezaian returns home
    Freed reporter Jason Rezaian returns home

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    Iran has also released a number of prisoners, but that has not required high-profile emissaries. In 2016, for instance, Iran released four prisoners -- including Saeed Abedini, Amir Mirzaei Hekmati and Post reporter Rezaian -- as part of a deal to free seven Iranians imprisoned in the US.
    Hikers Josh Fattal, center, Shane Bauer and his fiancée Sarah Shourd sit in Muscat International airport before flying home to the United States in 2011.
    Sarah Shourd, Shane Bauer and Joshua Fattal, three UC Berkeley graduates, had been hiking on the Iraq-Iran border when they were detained in July of 2009. Shourd was released in 2010, but the two men were kept in Iran until September of 2011. Their five-year sentences were commuted after payments of $500,000 for each of them.
    The most notorious hostage situation in US history is likely the Iran hostage crisis, which started in 1979 when 66 Americans were detained after the revolution that overthrew the Iranian government. The number eventually dropped to 52, but they were held by Iran for 444 days -- through a failed and disastrous rescue attempt -- until their negotiated release on January 20, 1981, the exact moment Ronald Reagan became President, and in exchange for the unfreezing of Iranian assets.