Complex sentence: Heyerdahl traveled to Azerbaijan four times (1981,1994,1999,2000) in support of his Odin theory, which was was rejected by historians, archaeologists, and linguists.
Split into simpler sentences: Heyerdahl traveled to Azerbaijan four times (1981,1994,1999,2000). Heyerdahl's Odin theory was rejected by historians, archaeologists, and linguists.