It's been 20 years since the city's handover from Britain to China.
Ruled by the British Crown following the Opium wars of the 19th century, on the expiration of the New Territories lease in 1997 all of Hong Kong was returned to China.
Part of that deal was democracy.
Hong Kong was to be allowed to continue its way of life for at least 50 years under a policy of 'one country, two systems'.
Eventual universal suffrage was also agreed.
But some in Hong Kong say China hasn't kept its end of the bargain.
The disappearance of the booksellers was a watershed moment for many, proving the city was no longer safe from mainland power.
Author and columnist Jason Ng says it intensified societal divisions established during the so-called 'umbrella' movement of 2014.
