Some few really significant dates in the history of psychology:
1879: Wilhelm Wundt in Leipzig, Germany, founds the first laboratory dedicated to psychology, separating psychology from philosophy for the first time.
1913: John Broadus Watson declares that to be a science, psychology must only study the observable and thus must be a science of behavior, rather than of mind; this inaugurates roughly six decades of dominance of American psychology by Behaviorism.
1967: (an arbitrary date for the beginning of Cognitive Psychology:) Ulric Neisser publishes his textbook called Cognitive Psychology, outlining the areas of study (e.g., attention, memory, perception, language) that had begun yielding to investigation in the decade previous and presenting a consensus view of the new field that solidified its popularity and led to its rapid ascendance.

Outline of Epistemology for Psychology: