1. In 1862, President Abraham Lincoln issued an order authorizing the enlistment of African American soldiers in the Union Army. This order paved the way for the formation of the United States Colored Troops, which played a significant role in the Union's victory in the Civil War.

2. In 1891, the International Conference on Weights and Measures adopted the metric system as the standard system of measurement. The United States adopted the metric system in 1975, but it has not been widely adopted in everyday use.

3. In 1920, the 19th Amendment to the U.S. Constitution was ratified, guaranteeing women the right to vote. This was a major milestone in the struggle for gender equality and opened the door for women to participate fully in the political process.

4. In 2005, Hurricane Katrina made landfall in New Orleans, causing widespread devastation and loss of life. The storm was one of the costliest natural disasters in U.S. history and raised many questions about the preparedness and response of local and federal authorities.

5. In 2016, the Smithsonian National Museum of African American History and Culture opened to the public in Washington, D.C. The museum houses a vast collection of artifacts and exhibits exploring the history and culture of African Americans, from slavery to the present day. Its opening was a major milestone in the recognition and celebration of African American contributions to American history and culture.