Complex sentence: Central America is the tapering isthmus of southern North America, with unique and varied features extending from the north-western borders of Belize and Guatemala southeastward to the Isthmus of Panama where it connects to the Pacific Lowlands in northwestern South America.
Split into simpler sentences: Central America is the tapering isthmus of southern North America, with unique and varied geographic features. The landmass extends southeastward to the Isthmus of Panama, where it connects to the Pacific Lowlands in northwestern South America.