Complex sentence: Arias' party regained power after the U.S. invasion of Panama a year later; its presidential candidate, Guillermo Endara, had won elections earlier that year, only to have them annulled by Noriega.
Split into simpler sentences: Arias' party regained power after the U.S. invasion of Panama a year later. Its presidential candidate, Guillermo Endara, had won elections earlier that year, only to have them annulled by Noriega.