Complex sentence: According to western leadership, GRU Spetsnaz spearheaded the occupation of the Crimean peninsula during the 2014 Crimean crisis, with several hundred members of the GRU 45th Spetsnaz Regiment and the 22nd Spetsnaz brigade sent in, disguised as civilians.
Split into simpler sentences: According to western leadership, GRU Spetsnaz spearheaded the occupation of the Crimean peninsula during the 2014 Crimean crisis. Allegedly, several hundred members of the GRU 45th Spetsnaz Regiment and the 22nd Spetsnaz brigade were then sent in, disguised as civilians.