Complex sentence: The 1990s in Hong Kong was defined by the 1984 Sino-British Joint Declaration that made way for a series of changes to prepare for the handover from Britain to China.
Split into simpler sentences: The 1990s in Hong Kong started with the future of Hong Kong decided in the Sino-British Joint Declaration. Under this background, Hong Kong made its way in a series of changes to prepare for the handover from Britain to China.