1. The Great Anthracite Strike of 1902 began on May 18th, when over 140,000 coal miners went on strike in Pennsylvania to demand better working conditions and higher wages. The strike lasted for months and had significant implications for the labor movement in the United States.

2. On May 18th, 1940, the Allegheny County Courthouse in Pittsburgh was bombed by members of an anarchist group known as the "People's Commandos". The bombing caused significant damage, but no one was injured. The incident remains one of the most notorious political bombings in Pennsylvania's history.

3. The Pennsylvania State University was founded on May 18, 1855, as the Farmers' High School of Pennsylvania. The school has grown to become one of the largest universities in the United States, with more than 97,000 students enrolled across its 24 campuses.

4. The Battle of Spotsylvania Court House began on May 18th, 1864, during the American Civil War. The battle was waged between Union and Confederate forces in Virginia and lasted for nearly two weeks. Although both sides suffered significant casualties, the Union eventually emerged victorious.

5. On May 18th, 1980, the eruption of Mount St. Helens in Washington state caused an ash cloud that reached as far east as Pennsylvania. The incident had a significant impact on the environment and economy of the region, with many businesses and industries affected by the ashfall.