Complex sentence: The Court Case which lasted 20 years, and complicated by the death of one of the defendants, involved the matter whereby the defendant had committed a trespass to land of his neighbor by tunneling under the plaintiffs' land and mining coal from the plaintifs land.
Split into simpler sentences: The court case lasted 20 years, and was complicated by the death of one of the defendants. It involved a matter in which the defendant had committed a trespass to land of his neighbor by tunneling under the plaintiffs' land and mining coal from the plaintifs land.