Complex sentence: Looting in Mesoamerica has a long tradition and history, many graves are looted before the archaeologists could reach them, and the artifacts are then sold to wealthy collectors in the United States, Japan or Europe.
Split into simpler sentences: Looting in Mesoamerica has a long tradition and history. Graves are often looted before the archaeologists can reach them, and the artifacts are then sold to wealthy collectors in the United States, Japan, or Europe.