On the Internet, it helps to find the domains of museum websites, archives, documentary/television productions, libraries, and educational and historic organizations, whose work is accurately identifying archival items (photographs, posters, artifacts, etc.).
You might do the following Google Search:
TOPIC + TIMELINE
TOPIC + CHRONOLOGY
e.g. Women's History Timeline;
Civil War Timeline
Important!: There are many well meaning enthusiast sites on the web. In particular, there has also been an explosion of infographic and meme-type content designed to amuse and entertain that may be inaccurate. You must verify any information you find with a reliable source. (See the "Evaluating Sources" tab above).