Complex sentence: Since Jefferson's wife Martha had died two years previous, friends noted that the widower Jefferson seemed so depressed that he might be suicidal and believed that sending him to France would also take his mind off his wife's death.
Split into simpler sentences: Since Jefferson's wife Martha had died two years previous, friends noted that the widower Jefferson seemed so depressed that he might be suicidal. They believed that sending him to France would take his mind off his wife's death.