Complex sentence: By the end of April 1945 an anti-fascist general uprising had errupted in all the northern cities, co-ordinated by the CLNAI ("Comitato di Liberazione Nazionale Alta Italia"), the collective political-military leadership of the main partisan groups operating in northern Italy.
Split into simpler sentences: By the end of the month a general uprising had errupted in all the northern cities. The uprising was led by the CLNAI ("Comitato di Liberazione Nazionale Alta Italia"), the collective political-military leadership of the main partisan groups operating in northern Italy.