How were previous US detainees in North Korea released?

North Korea has a history of detaining Americans and using them as bargaining chips against the United States.President Donald Trump tweeted Wednesday to "stay tuned" for news on the three Americans detained in North Korea, raising hopes for their release before a summit between Trump and North Korean leader Kim Jong Un in the coming weeks.Former US president Bill Clinton made a trip to Pyongyang in 2009 to secure the release of journalists Laura Ling and Euna Lee, who were sentenced to 12 years