Complex sentence: By the time of the American Civil War, as telegraph traffic increased, the Grove cell's tendency to discharge poisonous nitrogen dioxide (NO 2) fumes proved increasingly hazardous to health, and as telegraphs became more complex, the need for constant voltage became critical.
Split into simpler sentences: By the time of the American Civil War, as telegraph traffic increased, the Grove cell's tendency to discharge poisonous nitrogen dioxide (NO 2) fumes proved increasingly hazardous to health. However, as telegraphs became more complex, the need for constant voltage became critical.