From Captain America: The Winter Soldier
Dr. Arnim Zola
HYDRA was founded on the belief that humanity could not be trusted with its own freedom. What we did not realize was that if you tried to take that freedom, they resist. The war taught us much. Humanity needed to surrender its freedom willingly. After the war, S.H.I.E.L.D. was founded, and I was recruited. The new HYDRA grew, a beautiful parasite inside S.H.I.E.L.D. For 70 years, HYDRA has been secretly feeding crises, reaping war. And when history did not cooperate, history was changed.
That's impossible. S.H.I.E.L.D. would've stopped you.