Complex sentence: Perhaps the most significant occurrence in Lovecraft's involvement with UAPA though is when he published one of his earlier attempts at weird fiction, "The Alchemist", in the main UAPA journal in 1916.
Split into simpler sentences: Perhaps the most significant occurrence in Lovecraft's involvement with UAPA though is his beginning to published his attempts at weird fiction. This started with "The Alchemist", published in the main UAPA journal in 1916.