1. On June 21, 1836, Arkansas became the 25th state to join the United States of America. This historic event marked the end of a long process of territorial expansion and the beginning of a new era of statehood for the people of Arkansas.

2. In 1957, on June 21, the US Supreme Court ruled on the historic case of Cooper v. Aaron. The case involved the Little Rock Nine, a group of African American students who were attempting to integrate into an all-white high school in Little Rock, Arkansas. The Supreme Court's ruling affirmed the principle of federal supremacy in constitutional interpretation, and helped to advance the cause of civil rights in the United States.

3. On June 21, 1964, President Lyndon B. Johnson signed the Civil Rights Act of 1964 into law. This landmark legislation prohibited discrimination on the basis of race, color, religion, or national origin in many areas of public life, including employment, education, and housing. The Civil Rights Act of 1964 was a significant achievement for the civil rights movement, and helped to further the cause of equality and justice in America.

4. On June 21, 1996, the Arkansas River flooded, causing significant damage and loss of life in several communities along its path. The flooding was caused by severe storms and heavy rainfall, and resulted in billions of dollars in property damage and numerous fatalities.

5. On June 21, 2000, the United States Supreme Court issued a landmark ruling in the case of United States v. Morrison. The case involved the constitutionality of the Violence Against Women Act, which had been passed by Congress in 1994. The Supreme Court ruled that the act was unconstitutional, stating that the Commerce Clause of the Constitution did not give Congress the authority to regulate non-commercial, criminal activity based solely on gender. This decision had significant implications for the scope of federal power and the protection of women's rights.