Is this a run-on sentence?
During the Civil War, the Union blocked the port of New Orleans, preventing the shipment of coffee, devoted coffee drinkers began mixing chicory with their coffee to make it last longer.
A: no
B: yes
This is a run-on sentence. It is a comma splice formed from two sentences run together, joined by just a comma.
During the Civil War, the Union blocked the port of New Orleans, preventing the shipment of coffee, devoted coffee drinkers began mixing chicory with their coffee to make it last longer.
Here is one way to fix the run-on sentence:
During the Civil War, the Union blocked the port of New Orleans, preventing the shipment of coffee. As a result, devoted coffee drinkers began mixing chicory with their coffee to make it last longer.