Complex sentence: His fourth novel "War Machine" was published in 2007 by Solaris Books, which were then followed by "BioHell", "Hardcore" and "Cloneworld", also in the Combat K universe.
Split into simpler sentences: His fourth novel, "War Machine", was published in 2007 by Solaris Books. This was followed by "BioHell", "Hardcore" and "Cloneworld", also in the Combat K universe.