1. On June 18, 1776, Maryland became the seventh state to ratify the Declaration of Independence, paving the way for the United States to become a sovereign nation.

2. On June 18, 1812, the United States declared war on Great Britain, beginning the War of 1812. Maryland played a significant role in the conflict, with many of its citizens serving in the military and its coastal cities facing British attacks.

3. On June 18, 1863, Union General Benjamin F. Butler arrived in Baltimore and assumed command of the Department of the Monongahela, which included Maryland, West Virginia, and parts of Pennsylvania and Ohio.

4. On June 18, 1959, the Chesapeake Bay Bridge opened to traffic, connecting Maryland's Eastern and Western shores for the first time. The bridge spans 4.3 miles across the Chesapeake Bay and remains an iconic landmark in the state.

5. On June 18, 2015, the U.S. Supreme Court ruled in favor of upholding the Affordable Care Act, also known as Obamacare. The decision had significant impacts on Maryland's healthcare system, which had been at the forefront of implementing the law and expanding access to affordable health insurance.