What happened
The immediate trigger was procedural rather than substantive on its face: KMT legislator Chang Ching-chung announced the CSSTA had cleared committee review in under 30 seconds, without the item-by-item scrutiny opposition lawmakers and civic groups had been promised, on the grounds that the review period had technically expired. Protesters and a broad section of Taiwanese civil society read this as a deliberate procedural manoeuvre to ram through a substantively important agreement — one they worried would give Beijing significant economic leverage over Taiwanese service industries including publishing, healthcare, and telecommunications — without the scrutiny such a consequential trade pact with China specifically warranted, given the asymmetry in size and political intent between the two economies.
The protesters' three-week occupation of the main legislative chamber was almost entirely non-violent and ended through negotiation, with Legislative Speaker Wang Jin-pyng ultimately promising to hold off on the CSSTA until a broader cross-strait agreement oversight law was passed — a commitment that effectively killed the pact, which remains unratified over a decade later. The separate, roughly contemporaneous occupation of the Executive Yuan (the premier's office, a different and more sensitive building) was cleared by around 1,000 riot police using water cannon and batons against protesters who were, by most independent accounts including international media on the scene, not engaged in comparable force against police at that stage of the standoff.
The movement's lasting political effect was significant: it produced the New Power Party, a new pro-independence party that won seats in 2016, and is widely credited by Taiwanese political historians with hardening public opinion against closer economic integration with China in a way that shaped the DPP's landslide win under Tsai Ing-wen just two years later.