Complex sentence: Derived from veterns of the American Civil War, a Fenian army was also and in March of 1868,100,000 Fenian members held an anti-English demonstration in New York.
Split into simpler sentences: Derived from veterns of the American Civil War, a Fenian army was also formed. In March of 1868,100,000 Fenian members held an anti-English demonstration in New York.