It has used real-life events and the makers have gone to great lengths to make the action and setting as realistic as possible. The show is based on a very popular Israeli show called Hatufim, meaning 'prisoners of war', which was praised for its believable depiction of the way the security forces operate and the mindset that you might find in a long-term prisoner after being released.
In fact though, an event which seems very similar tot he original show, the release of real-life Israeli prisoner of war Gilad Shalit, did not take place until October 2011, by which time Homeland was already aired in the US and Hatufim had been running for some time. Shalit was a soldier who had been kept prisoner by Hamas for 5 years in exchange for a large number of Palestinian prisoners. Other events, like high profile assassination attempts, have also seemed to echo the series, but have mainly taken place after it was made and not before.
It is probably a sign of how realistic both the Israeli and US shows are, that many people do assume they are based directly on true stories.