Complex sentence: Glen Campbell, a vastly influential country guitarist and vocalist from the 1960s onward, announced in 2011 that he was suffering from Alzheimer's disease; upon the completion of a farewell tour, he retired from show business.
Split into simpler sentences: Glen Campbell, a vastly influential country guitarist and vocalist from the 1960s onward, announced in 2011 that he was suffering from Alzheimer's disease. Upon the completion of a farewell tour, he retired from show business.