Alexander Pierce had won? He wasn't the overall head of HYDRA.
Nobody was. It was organized into different cells. "Cut off one limb and two more shall grow in its place." (Although it really should be "one head" for the mythological reference to work.)
What I mean, though, is that the divergence point is apparently the end of The Winter Soldier. As we learned in TWS, Hydra had been quietly infiltrating SHIELD for decades. At the time of the movie, Alexander Pierce was the highest-level Hydra operative within SHIELD, and he was responsible for Project Insight, the algorithm that would've let Hydra identify and assassinate all potential threats to their power (including President Ellis, Tony Stark, Steve Rogers, and Stephen Strange for some reason), giving them free rein to take over SHIELD and the world openly. What we appeared to see at the end of the episode -- the former SHIELD headquarters still intact and overtly displaying the Hydra symbol -- implies that we're seeing the world that would've resulted if Project Insight, and thus Pierce, had succeeded.