Complex sentence: Some authors and the original researchers Ivanov and Toporov believe, the abduction of Mokosh causes the struggle, although Ivanov and Toporov nowhere quote original sources indicating that fact.
Split into simpler sentences: Some authors and the original researchers Ivanov and Toporov believe, the abduction of Mokosh causes the struggle. Though it should be noted that Ivanov and Toporov nowhere quote original sources indicating that fact.