1. On April 12, 1861, the Civil War began when the Confederate Army fired on Fort Sumter in South Carolina. Maryland, a border state between the Union and Confederacy, played a significant role in the conflict with battles and strategic locations such as Fort McHenry.

2. On April 12, 1963, civil rights leader Dr. Martin Luther King Jr. was arrested in Birmingham, Alabama and wrote his famous "Letter from Birmingham Jail." Maryland, which struggled with high levels of segregation and discrimination in the 1960s, played an important role in the civil rights movement.

3. On April 12, 1980, the Orioles baseball team opened their season at Memorial Stadium. The team, which had won the World Series just two years prior, defeated the Kansas City Royals 5-3 in their home opener.

4. On April 12, 2007, the Johns Hopkins Hospital in Baltimore became the first hospital in the United States to perform a transplant of an organ from a living HIV-positive donor to an HIV-positive recipient. This groundbreaking surgery signaled a new era in HIV organ donation and transplantation.

5. On April 12, 2015, Maryland governor Larry Hogan declared a state of emergency in Baltimore following protests and riots over the death of Freddie Gray, a black man who died in police custody. Maryland's history of racial tensions and police brutality continued to be a major issue in the state, even in the 21st century.