Complex sentence: Since 2002 the violence decreased significantly, with some paramilitary groups demobilizing as part of a controversial peace process and the guerrillas lost control of much of the territory they had once dominated.
Split into simpler sentences: Since 2002 the violence has decreased significantly, with some paramilitary groups demobilizing as part of a controversial peace process. As a result, the guerrillas lost control of much of the territory they had once dominated.