Complex sentence: In the early 1860s near the beginning of the Civil War, a high level of tension pervaded many counties in Pennsylvania owing to the fact that the county supported the Democratic Party while the Republican Abraham Lincoln served as president of the United States.
Split into simpler sentences: In the early 1860s, near the beginning of the Civil War, a high level of tension pervaded many counties in Pennsylvania. This was because the county supported the Democratic Party while the Republican Abraham Lincoln served as president of the United States.