Complex sentence: Gleb Uspensky wrote a letter demanding to stop publishing these slanderous pieces, documents emerged showing indeed that what Uspensky wrote about Nekrasov was untrue and the series abruptly stopped.
Split into simpler sentences: Gleb Uspensky wrote a letter demanding to stop publishing these slanderous pieces. Documents emerged showing that what Uspensky has written about Nekrasov was indeed untrue and the series abruptly stopped.