1. In 1793, George Washington delivered the first State of the Union address to Congress in Philadelphia, Pennsylvania. This date fell on January 21 that year because the official start of the congressional term was originally in March.

2. In 1865, the 13th Amendment to the U.S. Constitution was ratified, officially banning slavery and involuntary servitude throughout the United States. This historic event occurred on January 21 and marked the end of a long and painful chapter in American history.

3. In 1901, President McKinley held a reception at the White House, during which he greeted members of the diplomatic corps and other dignitaries. This event took place on January 21, just months before McKinley's assassination in September of that year.

4. In 1932, the United States declared itself officially opposed to the use of chemical warfare, a stance that would eventually develop into the Chemical Weapons Convention of 1993. This declaration was made on January 21 and reflected growing international concern about the use of chemical weapons in warfare.

5. In 2017, thousands of women gathered in Washington, D.C. for the Women's March on Washington, the largest single-day protest in U.S. history. This historic event occurred on January 21 and reflected widespread dissatisfaction with the newly inaugurated President Trump and his policies towards women, minorities, and other marginalized groups.